Naples, Italy

The National Institute of Astrophysics, Optics and Electronics is a Mexican science research institute located in Tonantzintla, Puebla. Founded by presidential decree on 11 November 1971, it has over 100 researchers in astrophysics, optics, electronics and computing science, with postgraduate programs in these areas. INAOE is one of 30 public research centers sponsored by the National Council of Science and Technology of Mexico . The Institute, in partnership with the University of Massachusetts Amherst, developed the Large Millimeter Telescope / Gran Telescopio Milimétrico on the Puebla-Veracruz border. Wikipedia.


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Bellazzini M.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2012

I briefly explore some relevant connections and differences between the evolutionary paths of dwarf galaxies and globular clusters. © 2015 International Astronomical Union.


Govoni F.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2012

The presence of μG-level magnetic fields associated with the intracluster medium of galaxy clusters is now widely acknowledged. Our knowledge of their properties has greatly improved in the recent years thanks to both new radio observations and the developments of new techniques to interpret data. © 2015 International Astronomical Union.


Mennella V.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2012

The physical properties of carbonaceous nanoparticles depend on the production conditions. In addition, these properties are modified by heat, UV and ion irradiation and gas interaction. We will discuss the synthesis and transformation of carbon nanoparticles that have been proposed as carriers of aromatic and aliphatic spectroscopic features observed in the interstellar medium. © 2015 International Astronomical Union.


Cassisi S.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2012

In these last years a huge amount of both spectroscopical and photometric data has provided a plain evidence of the fact that Galactic globular clusters (GCs) host various stellar sub-populations characterized by peculiar chemical patterns. The need of properly interpreting the various observational features observed in the Color-Magnitude Diagrams (CMDs) of these stellar systems requires a new generation of stellar models properly accounting for these chemical peculiarities both in the stellar model computations and in the color - Teff transformations. In this review we discuss the evolutionary framework that is mandatory in order to trace the various sub-populations in any given GC. © 2015 International Astronomical Union.


De Michelis P.,Italian National Institute of Geophysics and Volcanology | Tozzi R.,Italian National Institute of Geophysics and Volcanology | Consolini G.,National institute for astrophysics
Earth, Planets and Space | Year: 2017

From the very first measurements made by the magnetometers onboard Swarm satellites launched by European Space Agency (ESA) in late 2013, it emerged a discrepancy between scalar and vector measurements. An accurate analysis of this phenomenon brought to build an empirical model of the disturbance, highly correlated with the Sun incidence angle, and to correct vector data accordingly. The empirical model adopted by ESA results in a significant decrease in the amplitude of the disturbance affecting VFM measurements so greatly improving the vector magnetic data quality. This study is focused on the characterization of the difference between magnetic field intensity measured by the absolute scalar magnetometer (ASM) and that reconstructed using the vector field magnetometer (VFM) installed on Swarm constellation. Applying empirical mode decomposition method, we find the intrinsic mode functions (IMFs) associated with ASM-VFM total intensity differences obtained with data both uncorrected and corrected for the disturbance correlated with the Sun incidence angle. Surprisingly, no differences are found in the nature of the IMFs embedded in the analyzed signals, being these IMFs characterized by the same dominant periodicities before and after correction. The effect of correction manifests in the decrease in the energy associated with some IMFs contributing to corrected data. Some IMFs identified by analyzing the ASM-VFM intensity discrepancy are characterized by the same dominant periodicities of those obtained by analyzing the temperature fluctuations of the VFM electronic unit. Thus, the disturbance correlated with the Sun incidence angle could be still present in the corrected magnetic data. Furthermore, the ASM-VFM total intensity difference and the VFM electronic unit temperature display a maximal shared information with a time delay that depends on local time. Taken together, these findings may help to relate the features of the observed VFM-ASM total intensity difference to the physical characteristics of the real disturbance thus contributing to improve the empirical model proposed for the correction of data. © 2017 The Author(s).


Marano D.,National institute for astrophysics | Dario Grasso A.,University of Catania
2016 IEEE International Conference on Electronics, Circuits and Systems, ICECS 2016 | Year: 2016

In this paper, the traditional equivalent electrical model of silicon photomultipliers (SiPMs) is profitably extended to include the important effects of the read-out electronics on the shape of the output pulse waveforms. An improved analytical expression has been developed, which accurately reproduces the fast detector ignition, the avalanche self-quenching and the slow recharging operations, also taking into account both loading effect and bandwidth limitation of the coupled front-end. By means of the adopted analytical model, the SiPM dynamic response can be accurately mimicked and predicted, and reliable simulations can be also performed. Experimental tests on real detection systems corroborate the SiPM model and analytical results. © 2016 IEEE.


Damasso M.,National institute for astrophysics | Del Sordo F.,Yale University | Del Sordo F.,University of Stockholm
Astronomy and Astrophysics | Year: 2017

Context. The detection and characterisation of Earth-like planets with Doppler signals of the order of 1 m s-1 currently represent one of the greatest challenge for extrasolar-planet hunters. As results for such findings are often controversial, it is desirable to provide independent confirmations of the discoveries. Testing different models for the suppression of non-Keplerian stellar signals usually plaguing radial velocity data is essential to ensuring findings are robust and reproducible. Aims. Using an alternative treatment of the stellar noise to that discussed in the discovery paper, we re-analyse the radial velocity dataset that led to the detection of a candidate terrestrial planet orbiting the star Proxima Centauri. We aim to confirm the existence of this outstanding planet, and test the existence of a second planetary signal. Methods. Our technique jointly modelled Keplerian signals and residual correlated signals in radial velocities using Gaussian processes. We analysed only radial velocity measurements without including other ancillary data in the fitting procedure. In a second step, we have compared our outputs with results coming from photometry, to provide a consistent physical interpretation. Our analysis was performed in a Bayesian framework to quantify the robustness of our findings. Results. We show that the correlated noise can be successfully modelled as a Gaussian process regression, and contains a periodic term modulated on the stellar rotation period and characterised by an evolutionary timescale of the order of one year. Both findings appear to be robust when compared with results obtained from archival photometry, thus providing a reliable description of the noise properties. We confirm the existence of a coherent signal described by a Keplerian orbit equation that can be attributed to the planet Proxima b, and provide an independent estimate of the planetary parameters. Our Bayesian analysis dismisses the existence of a second planetary signal in the present dataset. © ESO, 2017.


Jafarzadeh S.,University of Oslo | Solanki S.K.,Max Planck Institute for Solar System Research | Solanki S.K.,Kyung Hee University | Stangalini M.,National institute for astrophysics | And 4 more authors.
Astrophysical Journal, Supplement Series | Year: 2017

We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300 nm and the Ca ii H 396.8 nm passbands of the filter imager on board the Sunrise balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are also obtained. Both compressible and incompressible (kink) waves are found in the small-scale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450 ± 100 km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29 ± 2 km s-1 and 31 ± 2 km s-1, respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed. © 2017. The American Astronomical Society. All rights reserved..


Chieffi A.,Instituto Nazionale Of Astrofisica | Chieffi A.,Monash University | Limongi M.,National institute for astrophysics | Limongi M.,University of Tokyo
Astrophysical Journal | Year: 2017

We discuss the influence of rotation on the combined synthesis of 44Ti and 56Ni in massive stars. While 56Ni is significantly produced by both complete and incomplete explosive Si burning, 44Ti is mainly produced by complete explosive Si burning, with a minor contribution (in standard non-rotating models) from incomplete explosive Si burning and O burning (both explosive and hydrostatic). We find that, in most cases, the thickness of the region exposed to incomplete explosive Si burning increases in rotating models (initial velocity, vini =300 kms-1) and since 56Ni is significantly produced in this zone, the fraction of mass coming from the complete explosive Si burning zone necessary to get the required amount of 56Ni reduces. Therefore the amount of 44Ti ejected for a given fixed amount of 56Ni decreases in rotating models. However, some rotating models at [Fe/H] = -1 develop a very extended O convective shell in which a consistent amount of 44Ti is formed, preserved, and ejected in the interstellar medium. Hence a better modeling of the thermal instabilities (convection) in the advanced burning phases together with a critical analysis of the cross sections of the nuclear reactions operating in O burning are relevant for the understanding of the synthesis of 44Ti. © 2017. The American Astronomical Society. All rights reserved.


Palma I.D.,National Institute of Nuclear Physics, Italy | Palma I.D.,University of Rome La Sapienza | Guetta D.,National institute for astrophysics | Amato E.,National institute for astrophysics
Astrophysical Journal | Year: 2017

Several pulsar wind nebulae (PWN) have been detected in the TeV band in the last decade. TeV emission is typically interpreted in a purely leptonic scenario, but this often requires that the magnetic field in the nebula be much lower than the equipartition value, as well as the assumption of an enhanced density of target radiation at IR frequencies. In this work, we consider the possibility that, in addition to the relativistic electrons and positrons, relativistic hadrons are also present in these nebulae. Assuming that some of the emitted TeV photons are of hadronic origin, we compute the associated flux of ∼1-100 TeV neutrinos. We use IceCube non-detection to put constraints on the fraction of TeV photons that might be contributed by hadrons and estimate the number of neutrino events that can be expected from these sources in ANTARES and KM3Net. © 2017, The American Astronomical Society. All rights reserved.


Vazza F.,Hamburger Sternwarte | Jones T.W.,University of Minnesota | Bruggen M.,Hamburger Sternwarte | Brunetti G.,National institute for astrophysics | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

Turbulence is a key ingredient for the evolution of the intracluster medium, whose properties can be predicted with high-resolution numerical simulations. We present initial results on the generation of solenoidal and compressive turbulence in the intracluster medium during the formation of a small-size cluster using highly resolved, non-radiative cosmological simulations, with a refined monitoring in time. In this first of a series of papers, we closely look at one simulated cluster whose formation was distinguished by a merger around z ~ 0.3.We separate laminar gas motions, turbulence and shocks with dedicated filtering strategies and distinguish the solenoidal and compressive components of the gas flows using Hodge-Helmholtz decomposition. Solenoidal turbulence dominates the dissipation of turbulent motions (~95 per cent) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important (~30 per cent of the total) only at large radii (≥0.5rvir) and close to merger events.We show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence. All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive, stretching and advective terms) are found to be significant, but in amounts that vary with time and location. Two important trends for the growth of enstrophy in our simulation are identified: first, enstrophy is continuously accreted into the cluster from the outside, and most of that accreted enstrophy is generated near the outer accretion shocks by baroclinic and compressive processes. Secondly, in the cluster interior vortex, stretching is dominant, although the other terms also contribute substantially. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Mignani R.P.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Mignani R.P.,University of Zielona Gora | Testa V.,National institute for astrophysics | Gonzalez Caniulef D.,University College London | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

The 'Magnificent Seven' (M7) are a group of radio-quiet isolated neutron stars discovered in the soft X-rays through their purely thermal surface emission. Owing to the large inferred magnetic fields (B ≈ 1013 G), radiation from these sources is expected to be substantially polarized, independently of the mechanism actually responsible for the thermal emission. A large observed polarization degree (PD) is, however, expected only if quantum-electrodynamic (QED) polarization effects are present in the magnetized vacuum around the star. The detection of a strong linearly polarized signal would therefore provide the first observational evidence of QED effects in the strong-field regime. While polarization measurements in the soft X-rays are not feasible yet, optical polarization measurements are within reach also for quite faint targets, like the M7 which have optical counterparts with magnitudes ≈26-28. Here, we report on the measurement of optical linear polarization for the prototype, and brightest member, of the class, RX J1856.5-3754 (V ~ 25.5), the first ever for one of the M7, obtained with the Very Large Telescope.We measured a PD = 16.43 ± 5.26 per cent and a polarization position angle PA = 145. ° 39 ± 9. ° 44, computed east of the North Celestial Meridian. The PD that we derive is large enough to support the presence of vacuum birefringence, as predicted by QED. © 2016 The Authors.


Campana R.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Maselli A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Bernieri E.,Third University of Rome | Massaro E.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2017

We report the detection of two new γ -ray sources in the Fermi-Large Area Telescope sky (Pass 8) at energies higher than 20 GeV and confirmed at lower energies, using a source detection tool based on the Minimum Spanning Tree algorithm. One of these sources, at a Galactic latitude of about -4°, is a new discovery, while the other was previously reported above 50 GeV in the 2FHL catalogue. We searched for archival multiwavelength data of possible counterparts and found interesting candidates. Both objects are radio sources and their Wide-field Infrared Survey Explorer infrared colours are typical of blazars. While, for the former source, no optical spectra are available, for the latter, a puzzling optical spectrum corresponding to a white dwarf star is found in the 6dF data base.We discuss the spectral energy distributions of both sources and possible interpretations. © 2016 The Authors.


Gualandris A.,University of Surrey | Read J.I.,University of Surrey | Dehnen W.,University of Leicester | Bortolas E.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2017

Coalescing massive black hole binaries, formed during galaxy mergers, are expected to be a primary source of low-frequency gravitational waves. Yet in isolated gas-free spherical stellar systems, the hardening of the binary stalls at parsec-scale separations owing to the inefficiency of relaxation-driven loss-cone refilling. Repopulation via collisionless orbit diffusion in triaxial systems is more efficient, but published simulation results are contradictory. While sustained hardening has been reported in simulations of galaxy mergers with N ~ 106 stars and in early simulations of rotating models, in isolated non-rotating triaxial models the hardening rate continues to fall with increasing N, a signature of spurious two-body relaxation. We present a novel approach for studying loss-cone repopulation in galactic nuclei. Since losscone repopulation in triaxial systems owes to orbit diffusion, it is a purely collisionless phenomenon and can be studied with an approximated force calculation technique, provided the force errors are well behaved and sufficiently small. We achieve this using an accurate fast multipole method and define a proxy for the hardening rate that depends only on stellar angular momenta. We find that the loss cone is efficiently replenished even in very mildly triaxial models (with axis ratios 1:0.9:0.8). Such triaxiality is unavoidable following galactic mergers and can drive binaries into the gravitational wave regime. We conclude that there is no 'final parsec problem'. © 2016 The Authors.


Gioannini L.,University of Trieste | Matteucci F.,University of Trieste | Matteucci F.,National institute for astrophysics | Matteucci F.,National Institute of Nuclear Physics, Italy | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

We present a galactic chemical evolution model which adopts updated prescriptions for all the main processes governing the dust cycle. We follow in detail the evolution of the abundances of several chemical species (C, O, S, Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The dwarf irregular galaxy is assumed to evolve with a low but continuous level of star formation and experience galactic winds triggered by supernova (SN) explosions. We predict the evolution of the gas to dust ratio in such a galaxy and discuss critically the main processes involving dust, such as dust production by asymptotic giant branch stars and Type II SNe, destruction and accretion (gas condensation in clouds).We then apply our model to damped Lyman α (DLA) systems which are believed to be dwarf irregulars, as witnessed by their abundance patterns. Our main conclusions are the following. (i) We can reproduce the observed gas to dust ratio in dwarf galaxies. (ii) We find that the process of dust accretion plays a fundamental role in the evolution of dust and in certain cases it becomes the dominant process in the dust cycle. On the other hand, dust destruction seems to be a negligible process in irregulars. (iii) Concerning DLA systems, we show that the observed gas-phase abundances of silicon, normalized to volatile elements (zinc and sulfur), are in agreement with our model. (iv) The abundances of iron and silicon in DLA systems suggest that the two elements undergo a different history of dust formation and evolution. Our work casts light on the nature of ironrich dust: the observed depletion pattern of iron is well reproduced only when an additional source of iron dust is considered. Here we explore the possibility of a contribution from Type Ia SNe as well as an efficient accretion of iron nanoparticles. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Baldi M.,University of Bologna | Baldi M.,National institute for astrophysics | Baldi M.,National Institute of Nuclear Physics, Italy | Simpson F.,University of Barcelona
Monthly Notices of the Royal Astronomical Society | Year: 2017

Persisting tensions between the cosmological constraints derived from low-redshift probes and the ones obtained from temperature and polarization anisotropies of the cosmic microwave background (CMB) - although not yet providing compelling evidence against the Λcold dark matter model - seem to consistently indicate a slower growth of density perturbations as compared to the predictions of the standard cosmological scenario. Such behaviour is not easily accommodated by the simplest extensions of General Relativity, such as f(R) models, which generically predict an enhanced growth rate. In this work, we present the outcomes of a suite of large N-body simulations carried out in the context of a cosmological model featuring a non-vanishing scattering cross-section between the dark matter and the dark energy fields, for two different parametrizations of the dark energy equation of state. Our results indicate that these dark scattering models have very mild effects on many observables related to large-scale structures formation and evolution, while providing a significant suppression of the amplitude of linear density perturbations and the abundance of massive clusters. Our simulations therefore confirm that these models offer a promising route to alleviate existing tensions between low-redshift measurements and those of the CMB. © 2016 The Authors.


Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2017

The emergence of cosmic structure is commonly considered one of the most complex phenomena in nature. However, this complexity has never been defined nor measured in a quantitative and objective way. In this work, we propose a method to measure the information content of cosmic structure and to quantify the complexity that emerges from it, based on Information Theory. The emergence of complex evolutionary patterns is studied with a statistical symbolic analysis of the datastream produced by state-of-the-art cosmological simulations of forming galaxy clusters. This powerful approach allows us to measure how many bits of information is necessary to predict the evolution of energy fields in a statistical way, and it offers a simple way to quantify when, where and how the cosmic gas behaves in complex ways. The most complex behaviours are found in the peripheral regions of galaxy clusters, where supersonic flows drive shocks and large energy fluctuations over a few tens of million years. Describing the evolution of magnetic energy requires at least twice as large amount of bits as required for the other energy fields. When radiative cooling and feedback from galaxy formation are considered, the cosmic gas is overall found to double its degree of complexity. In the future, Cosmic Information Theory can significantly increase our understanding of the emergence of cosmic structure as it represents an innovative framework to design and analyse complex simulations of the Universe in a simple, yet powerful way. © 2016 The Authors.


Kowalski A.F.,University of Colorado at Boulder | Kowalski A.F.,University of Maryland University College | Kowalski A.F.,NASA | Allred J.C.,NASA | And 3 more authors.
Astrophysical Journal | Year: 2017

The 2014 March 29 X1 solar flare (SOL20140329T17:48) produced bright continuum emission in the far- and near-ultraviolet (NUV) and highly asymmetric chromospheric emission lines, providing long-sought constraints on the heating mechanisms of the lower atmosphere in solar flares. We analyze the continuum and emission line data from the Interface Region Imaging Spectrograph (IRIS) of the brightest flaring magnetic footpoints in this flare. We compare the NUV spectra of the brightest pixels to new radiative-hydrodynamic predictions calculated with the RADYN code using constraints on a nonthermal electron beam inferred from the collisional thick-target modeling of hard X-ray data from Reuven Ramaty High Energy Solar Spectroscopic Imager. We show that the atmospheric response to a high beam flux density satisfactorily achieves the observed continuum brightness in the NUV. The NUV continuum emission in this flare is consistent with hydrogen (Balmer) recombination radiation that originates from low optical depth in a dense chromospheric condensation and from the stationary beam-heated layers just below the condensation. A model producing two flaring regions (a condensation and stationary layers) in the lower atmosphere is also consistent with the asymmetric Fe ii chromospheric emission line profiles observed in the impulsive phase. © 2017. The American Astronomical Society. All rights reserved.


Orlando S.,National institute for astrophysics | Drake J.J.,Harvard - Smithsonian Center for Astrophysics | Miceli M.,National institute for astrophysics | Miceli M.,University of Palermo
Monthly Notices of the Royal Astronomical Society | Year: 2017

The symbiotic nova V745 Sco was observed in outburst on 2014 February 6. Its observations by the Chandra X-ray Observatory at days 16 and 17 have revealed a spectrum characterized by asymmetric and blueshifted emission lines.Herewe investigate the origin of these asymmetries through 3D hydrodynamic simulations describing the outburst during the first 20 d of evolution. The model takes into account thermal conduction and radiative cooling, and assumes that a blast wave propagates through an equatorial density enhancement (EDE). From these simulations, we synthesize the X-ray emission and derive the spectra as they would be observed with Chandra.We find that both the blast wave and the ejecta distribution are efficiently collimated in polar directions due to the presence of the EDE. The majority of the X-ray emission originates from the interaction of the blast with the EDE and is concentrated on the equatorial plane as a ring-like structure. Our 'best-fitting' model requires a mass of ejecta in the outburst Mej ≈ 3×10-7M ⊙ and an explosion energy Eb ≈ 3×1043 erg, and reproduces the distribution of emission measure versus temperature and the evolution of shock velocity and temperature inferred from the observations. The model predicts asymmetric and blueshifted line profiles similar to those observed and explains their origin as due to substantial X-ray absorption of redshifted emission by ejecta material. The comparison of predicted and observed Ne and O spectral line ratios reveals no signs of strong Ne enhancement and suggests that the progenitor is a CO white dwarf. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bisnovatyi-Kogan G.S.,University of Rome La Sapienza | Bisnovatyi-Kogan G.S.,National Research Nuclear University MEPhI | Giovannelli F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2017

Context. We develop models for time lag between the maxima of the source brightness in different wavelengths during a transient flash of luminosity that is connected with a short-period increase of the mass flux onto the central compact object. Aims. We derive a simple formula for finding the time delay among events in different wavelengths which is valid in general for all disk-accreting cosmic sources. We quantitatively also discuss a model for time-lag formation in active galactic nuclei (AGNs). Methods. In close binaries with accretion disks, the time lag is connected with effects of viscosity that define a radial motion of matter in the accretion disk. In AGN flashes, the infalling matter has a low angular momentum, and the time lag is defined by the free-fall time to the gravitating center. Results. We show the validity of these models by means of several examples of galactic and extragalactic accreting sources. © 2017 ESO.


Pallocchia G.,National institute for astrophysics | Laurenza M.,National institute for astrophysics | Consolini G.,National institute for astrophysics
Astrophysical Journal | Year: 2017

Some interplanetary shocks are associated with short-term and sharp particle flux enhancements near the shock front. Such intensity enhancements, known as shock-spike events (SSEs), represent a class of relatively energetic phenomena as they may extend to energies of some tens of MeV or even beyond. Here we present an SSE case study in order to shed light on the nature of the particle acceleration involved in this kind of event. Our observations refer to an SSE registered on 2011 October 3 at 22:23 UT, by STEREO B instrumentation when, at a heliocentric distance of 1.08 au, the spacecraft was swept by a perpendicular shock moving away from the Sun. The main finding from the data analysis is that a Weibull distribution represents a good fitting function to the measured particle spectrum over the energy range from 0.1 to 30 MeV. To interpret such an observational result, we provide a theoretical derivation of the Weibull spectrum in the framework of the acceleration by "killed" stochastic processes exhibiting power-law growth in time of the velocity expectation, such as the classical Fermi process. We find an overall coherence between the experimental values of the Weibull spectrum parameters and their physical meaning within the above scenario. Hence, our approach based on the Weibull distribution proves to be useful for understanding SSEs. With regard to the present event, we also provide an alternative explanation of the Weibull spectrum in terms of shock-surfing acceleration. © 2017. The American Astronomical Society. All rights reserved.


Romano P.,National institute for astrophysics | Falco M.,National institute for astrophysics | Guglielmino S.L.,University of Catania | Murabito M.,University of Catania
Astrophysical Journal | Year: 2017

We describe high-resolution observations of a GOES B-class flare characterized by a circular ribbon at the chromospheric level, corresponding to the network at the photospheric level. We interpret the flare as a consequence of a magnetic reconnection event that occurred at a three-dimensional (3D) coronal null point located above the supergranular cell. The potential field extrapolation of the photospheric magnetic field indicates that the circular chromospheric ribbon is cospatial with the fan footpoints, while the ribbons of the inner and outer spines look like compact kernels. We found new interesting observational aspects that need to be explained by models: (1) a loop corresponding to the outer spine became brighter a few minutes before the onset of the flare; (2) the circular ribbon was formed by several adjacent compact kernels characterized by a size of 1″-2″; (3) the kernels with a stronger intensity emission were located at the outer footpoint of the darker filaments, departing radially from the center of the supergranular cell; (4) these kernels started to brighten sequentially in clockwise direction; and (5) the site of the 3D null point and the shape of the outer spine were detected by RHESSI in the low-energy channel between 6.0 and 12.0 keV. Taking into account all these features and the length scales of the magnetic systems involved in the event, we argue that the low intensity of the flare may be ascribed to the low amount of magnetic flux and to its symmetric configuration. © 2017. The American Astronomical Society. All rights reserved..


Migliorini A.,National institute for astrophysics | De Sanctis M.C.,National institute for astrophysics | Lazzaro D.,Observatorio Nacional | Ammannito E.,University of California at Los Angeles
Monthly Notices of the Royal Astronomical Society | Year: 2017

We present new near-infrared (NIR) reflectance spectra of 10 V-type candidate asteroids obtained at the 3.6 m Telescopio Nazionale Galileo covering the spectral range of 0.7-2.5 μm. The observed objects were selected from diverse data sets of putative V-type asteroids in order to characterize them, and hence better understand their relationship with (4) Vesta. We derive spectral parameters from NIR spectra to infermineralogical information of the observed asteroids. All the spectra of the asteroids here reported showtwo prominent absorption features at 1 and 2 μmthat are typical of V-class objects. The comparison of spectral parameters such as band centres and band separation, among our observations, Howardites, Eucrites, Diogenites meteorites, and (4) Vesta from Visible and Infrared Spectrometer (VIR) data on Dawn reveals that there is a strong correlation between these objects. From our analysis, four objects are compatible with Howardites, three are more similar to a eucritic-like composition, and two are compatible with Diogenites. Asteroid 26145, which is the only member of the Vesta dynamical family observed in 2012 March, is compatible with Vesta's surface, and shows a composition close to the Eucrites. © 2016 The Authors.


Magrini L.,National institute for astrophysics | Goncalves D.R.,Federal University of Rio de Janeiro | Vajgel B.,Observatorio Nacional MCTI
Monthly Notices of the Royal Astronomical Society | Year: 2017

We present new spectroscopic observations obtained with Gemini Multi-Object Spectrographs at Gemini-South of a sample of 25 HII regions located in NGC 55, a late-type galaxy in the nearby Sculptor group. We derive physical conditions and chemical composition through the Te method for 18 HII regions, and strong-line abundances for 22 HII regions. We provide abundances of He, O, N, Ne, S and Ar, finding a substantially homogeneous composition in the ionized gas of the disc of NGC 55, with no trace of radial gradients. The oxygen abundances, both derived with Te and strong-line methods, have similar mean values and similarly small dispersions: 12+log (O/H) = 8.13 ± 0.18 dex with the former and 12+log (O/H) = 8.17 ± 0.13 dex with the latter. The average metallicities and the flat gradients agree with previous studies of smaller samples of HII regions and there is a qualitative agreement with the blue supergiant radial gradient as well. We investigate the origin of such flat gradients comparing NGC 55 with NGC 300, its companion galaxy, which is also twin of NGC 55 in terms of mass and luminosity. We suggest that the differences in the metal distributions in the two galaxies might be related to the differences in their K-band surface density profile. The flatter profile of NGC 55 probably causes in this galaxy higher infall/outflow rates than in similar galaxies. This likely provokes a strong mixing of gas and a re-distribution of metals. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Stift M.J.,Armagh Observatory | Leone F.,University of Catania | Leone F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2017

Empirical abundance maps derived with the help of Zeeman Doppler mapping are found to be at variance with the predictions of numerical models of atomic diffusion in magnetic atmospheres of ApBp stars. Although theory has often been made responsible for this lack of agreement, direct spectral synthesis based on the published abundance maps reveals that all the chemical inhomogeneities claimed for HD 3980 are entirely spurious, and those of HD 50773 to a large extent. In the former case, this is shown to be due to the neglect of a strong magnetic field, and in the latter case, due to noisy spectra in combination with considerable rotational broadening and ensuing strong line blending. Doppler maps for other magnetic ApBp stars could be affected by similar problems. It is also pointed out that the patchy, extreme overabundances in HD 3980 cannot be reconciled with the theory of stellar atmospheres. © 2016 The Authors.


Bragaglia A.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2015

The contribution of massive star clusters to their hosting halo dramatically depends on their formation mechanism and their early evolution. Massive globular clusters in the Milky Way (and in other galaxies) have been shown to display peculiar chemical patterns (light-elements correlations and anti-correlations) indicative of a complex star formation, confirmed by photometric evidence (spread or split sequences). I use these chemical signatures to try to understand what is the fraction of halo stars originally born in globular clusters. Copyright © International Astronomical Union 2017.


Decressin T.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2015

Spectroscopic and photometric evidences have led to a complete revision of our understanding of globular clusters with the discovery of multiple stellar populations which differ chemically. Whereas some stars have a chemical composition similar to fields stars, others show large star-To-star variations in light elements (Li to Al) while their composition in iron and heavy elements stay constant. This peculiar chemical pattern can be explained by self-pollution of the intracluster gas occurring in the early evolution of clusters. Here the possible impact from a first generation of fast rotating stars to the early evolution of globular clusters is presented. The high rotation velocity will allow the stars to rotate at the break-up velocity and release matter enrich in H-burning which in turn will produce new stars with a chemical composition in agreement with observations. The massive stars have also an important role to clear the cluster from the remaining gas left after the star formation episodes. If the gas expulsion is fast enough, the strong change in the potential well will lead to the loss of stars occupying the outer part of the cluster. As second generation stars are preferentially born in the cluster centre, the ratio of second to first generation stars will increase over time to match the present ratio determined by observations. Considerations on the properties of low-mass stars still present in globular clusters will also be presented. Copyright © 2017 International Astronomical Union.


Cassisi S.,National institute for astrophysics
Proceedings of the International Astronomical Union | Year: 2015

Recent spectroscopic and photometric surveys of Galactic Globular Clusters have shown that these stellar systems host distinct sub-populations of stars characterised by peculiar chemical patterns. In the following we wish to address the issue of how these specific chemical patterns affect both the structural and evolutionary properties of stars as well as their spectral energy distribution. The implications of these effects on the photometric appearance of multiple stellar populations in different photometric planes are also briefly discussed. Copyright © International Astronomical Union 2017.


Strazzulla G.,National institute for astrophysics | Brunetto R.,University Paris - Sud
Nuclear Physics News | Year: 2017

Around the 1970s the use of Van de Graaff type ion accelerators (mostly having voltages between 10 s of kV and 1–2 MV) became inadequate for nuclear physics that required higher and higher energies to remain at the forefront of the research in the field. In the same years, a number of analytical techniques were developed, such as Rutherford backscattering, channeling, and proton induced x-ray emission (PIXE) that using 1–2 MeV ion beams became a very appropriate and powerful means for the elemental analysis of materials and devices. These latter progressively became smaller and smaller, contributing to the development of present micro and nano technologies. It has also became clear that some properties of semiconductors (Silicon, Germanium), particularly electrical properties, are strongly dependent on the presence of dopants (e.g., Boron, Arsenic, Phosphorus) easily obtained by ion implantation. Nowadays particle accelerators are widely used in the science of materials both by academic institutions and industries. ©, Copyright Taylor & Francis.


Soffitta P.,National institute for astrophysics
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2017

XIPE, the X-ray Imaging Polarimetry Explorer, is a candidate ESA fourth medium size mission, now in competitive phase A, aimed at time-spectrally-spatially-resolved X-ray polarimetry of a large number of celestial sources as a breakthrough in high energy astrophysics and fundamental physics. Its payload consists of three X-ray optics with a total effective area larger than one XMM mirror but with a low mass and of three Gas Pixel Detectors at their focus. The focal length is 4. m and the whole satellite fits within the fairing of the Vega launcher without the need of an extendable bench. XIPE will be an observatory with 75% of the time devoted to a competitive guest observer program. Its consortium across Europe comprises Italy, Germany, Spain, United Kingdom, Switzerland, Poland, Sweden Until today, thanks to a dedicated experiment that dates back to the '70, only the Crab Nebula showed a non-zero polarization with large significance [1] in X-rays. XIPE, with its innovative detector, promises to make significative measurements on hundreds of celestial sources. © 2017 Elsevier B.V.


Capetti A.,National institute for astrophysics | Massaro F.,University of Turin | Baldi R.D.,University of Southampton
Astronomy and Astrophysics | Year: 2017

We built a catalog of 219 FR I radio galaxies (FR Is), called FRICAT, selected from a published sample and obtained by combining observations from the NVSS, FIRST, and SDSS surveys. We included in the catalog the sources with an edge-darkened radio morphology, redshift ≤ 0.15, and extending (at the sensitivity of the FIRST images) to a radius r larger than 30 kpc from the center of the host. We also selected an additional sample (sFRICAT) of 14 smaller (10 < r < 30 kpc) FR Is, limiting to z < 0.05. The hosts of the FRICAT sources are all luminous (-21 ≳ Mr ≳ -24), red early-type galaxies with black hole masses in the range 108 ≲ MBH ≲ 3 × 109 M⊙; the spectroscopic classification based on the optical emission line ratios indicates that they are all low excitation galaxies. Sources in the FRICAT are then indistinguishable from the FR Is belonging to the Third Cambridge Catalogue of Radio Sources (3C) on the basis of their optical properties. Conversely, while the 3C-FR Is show a strong positive trend between radio and [O III] emission line luminosity, these two quantities are unrelated in the FRICAT sources; at a given line luminosity, they show radio luminosities spanning about two orders of magnitude and extending to much lower ratios between radio and line power than 3C-FR Is. Our main conclusion is that the 3C-FR Is just represent the tip of the iceberg of a much larger and diverse population of FR Is. © 2017 ESO.


Ubertini P.,National institute for astrophysics
Proceedings of the International Astronautical Congress, IAC | Year: 2016

The history of space astronomy, especially in the past three decades, has demonstrated clearly the importance and benefit of access to the Gamma-ray, X-ray, UV-optical, near IR and far-IR spectrum from space. The combined use of large ground based facilities and large space observatories is playing a key role in the advance of astrophysics by providing access to the entire electromagnetic spectrum, allowing high sensitivity observations from the lower radio wavelength to the higher energy gamma rays. It is nowadays clear that a forward steps in the understanding of the Universe evolution and large scale structure formation is essential and only possible with the combined use of multi-wavelength imaging and spectral high resolution instruments. In fact, only a few 'Observatory Class' space missions are planned and there is a need to ensure proper ground facility coverage: the synergy Ground-Space is not escapable in the timeframe 2020-2030. Furthermore, the recent detection of Gravitational Waves by the LIGO-VIRGO consortia and contemporary observation in the electromagnetic bandwidth has opened a new window to study and understand the formation and evolution of the Universe. Things have profoundly changed over the last two years. Our access to astrophysical information is boosted by three new Astronomies: Gravitational Waves, High Energy Neutrinos and Ultra-High Energy Cosmic Rays are about to open new phase spaces - not only in Astronomy, but also in fundamental physic. In fact, one of the most important observational challenges of our time is to establish the link between discoveries of the new Astronomies and the electromagnetic Universe. This paper will provide an update of the worldwide scenario predicted for the next 2 decades in the field astronomical research to be exploited via Space and Ground and Space Large Scale facility in synergy.


Rothery D.A.,Open University Milton Keynes | Mancinelli P.,University of Perugia | Guzzetta L.,National institute for astrophysics | Wright J.,Open University Milton Keynes
Journal of Geophysical Research: Planets | Year: 2017

The smooth plains on the floor of Mercury's Caloris basin and those almost entirely surrounding it beyond its rim are usually accepted to be younger than the rim materials and to be lava flows rather than impact melt. High-resolution imaging shows that the emplacement of interior and exterior plains was concurrent, with evidence of both inward and outward flow while they were being emplaced. The Caloris rim is breached in two places by continuous smooth plains that seamlessly connect interior and exterior plains. The gross-scale spectral and compositional distinctiveness of interior and exterior plains is blurred on a scale of several tens of kilometers, which could reflect interfingering of flow units less than a few hundred kilometers long that tapped melt sources of different composition and/or depth inside and outside the basin followed by local mixing of regolith. Flows occurring both inside and outside the basin should be included in estimates of the total erupted volume. ©2017. The Authors.


Lipartito I.,Smith College | Judge P.G.,High Altitude Observatory | Reardon K.,U.S. National Solar Observatory | Reardon K.,Queen's University of Belfast | Cauzzi G.,National institute for astrophysics
Astrophysical Journal | Year: 2014

We recently reported extremely rapid changes in chromospheric fine structure observed using the IBIS instrument in the red wing of Hα. Here, we examine data obtained during the same observing run (2010 August 7), of a mature active region NOAA 11094. We analyze more IBIS data including wavelength scans and data from the Solar Dynamics Observatory, all from within a 30 minute interval. Using a slab radiative transfer model, we investigate the physical nature of fibrils in terms of tube-like versus sheet-like structures. Principal Component Analysis shows that the very rapid Hα variations in the line wings depend mostly on changes of line width and line shift, but for Ca II 854.2 the variations are dominated by changes in column densities. The tube model must be rejected for a small but significant class of fibrils undergoing very rapid changes. If our wing data arise from the same structures leading to "type II spicules," our analysis calls into question much recent work. Instead, the data do not reject the hypothesis that some fibrils are optical superpositions of plasma collected into sheets. We review how Parker's theory of tangential discontinuities naturally leads to plasma collecting into sheets, and show that the sheet picture is falsifiable. Chromospheric fine structures seem to be populated by both tubes and sheets. We assess the merits of spectral imaging versus slit spectroscopy for future studies. © 2014. The American Astronomical Society. All rights reserved.


Hendricks B.,University of Victoria | Stetson P.B.,National Research Council Canada | Vandenberg D.A.,University of Victoria | Dall'Ora M.,National institute for astrophysics
Astronomical Journal | Year: 2012

We have used a combination of broadband near-infrared and optical Johnson-Cousins photometry to study the dust properties in the line of sight to the Galactic globular cluster M4. We have investigated the reddening effects in terms of absolute strength and variation across the cluster field, as well as the shape of the reddening law defined by the type of dust. All three aspects had been poorly defined for this system and, consequently, there has been controversy about the absolute distance to this globular cluster, which is closest to the Sun. Here, we determine the ratio of absolute to selective extinction (R V) in the line of sight toward M4, which is known to be a useful indicator for the type of dust and therefore characterizes the applicable reddening law. Our method is independent of age assumptions and appears to be significantly more precise and accurate than previous approaches. We obtain A V /E(B - V) = 3.76 ± 0.07 (random error) for the dust in the line of sight to M4 for our set of filters. That corresponds to a dust-type parameter R V = 3.62 ± 0.07 in the Cardelli et al. reddening law. With this value, the distance to M4 is found to be 1.80 ± 0.05 kpc, corresponding to a true distance modulus of (m - M) 0 = 11.28 ± 0.06 (random error). A reddening map for M4 has been created, which reveals a spatial differential reddening of δE(B - V) ≥ 0.2 mag across the field within 10′ around the cluster center; this is about 50% of the total mean reddening, which we have determined to be E(B - V) = 0.37 ± 0.01. In order to provide accurate zero points for the extinction coefficients of our photometric filters, we investigated the impact of stellar parameters such as temperature, surface gravity, and metallicity on the extinction properties and the necessary corrections in different bandpasses. Using both synthetic ATLAS9 spectra and observed spectral energy distributions, we found similarly sized effects for the range of temperature and surface gravity typical of globular cluster stars: each causes a change of about 3% in the necessary correction factor for each filter combination. Interestingly, variations in the metallicity cause effects of the same order when the assumed value is changed from the solar metallicity ([Fe/H] = 0.0) to [Fe/H] = -2.5. The systematic differences between the reddening corrections for a typical main-sequence turnoff star in a metal poor globular cluster and a Vega-like star are even stronger (5%). We compared the results from synthetic spectra to those obtained with observed spectral energy distributions and found significant differences for temperatures lower than 5000 K. We have attributed these discrepancies to the inadequate treatment of some molecular bands in the B filter within the ATLAS9 models. Fortunately, these differences do not affect the principal astrophysical conclusions in this study, which are based on stars hotter than 5000K. From our calculations, we provide extinction zero points for Johnson-Cousins and Two Micron All Sky Survey filters, spanning a wide range of stellar parameters and dust types. These extinction tables are suited for accurate, object-specific extinction corrections. © 2012. The American Astronomical Society. All rights reserved.


Sneden C.,University of Texas at Austin | Sneden C.,Ege University | Lucatello S.,National institute for astrophysics | Ram R.S.,University of York | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

New red and violet system line lists for the CN isotopologues 13C14N and 12C15N have been generated. These new transition data are combined with those previously derived for 12C14N, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values. © 2014. The American Astronomical Society. All rights reserved..


Napolitano N.R.,National institute for astrophysics | Pota V.,Swinburne University of Technology | Romanowsky A.J.,San Jose State University | Romanowsky A.J.,University of California at Santa Cruz | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We study the mass and anisotropy distribution of the giant elliptical galaxy NGC 5846 using stars, as well as the red and blue globular cluster (GC) subpopulations. We break degeneracies in the dynamical models by taking advantage of the different phase space distributions of the two GC subpopulations to unambiguously constrain the mass of the galaxy and the anisotropy of the GC system. Red GCs show the same spatial distribution and behaviour as the starlight, whereas blue GCs have a shallower density profile, a larger velocity dispersion and a lower kurtosis, all of which suggest a different orbital distribution. We use a dispersion-kurtosis Jeans analysis and find that the solutions of separate analyses for the two GC subpopulations overlap in the halo parameter space. The solution converges on a massive dark matter halo, consistent with expectations from Λ cold dark matter (ΛCDM) and 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) cosmology in terms of virial mass (logMDM ~ 13.3M⊙) and concentration (cvir ~ 8). This is the first such analysis that solves the dynamics of the different GC subpopulations in a self-consistent manner. Our method improves the uncertainties on the halo parameter determination by a factor of 2 and opens new avenues for the use of elliptical galaxy dynamics as tests of predictions from cosmological simulations. The implied stellar mass-to-light ratio derived from the dynamical modelling is fully consistent with a Salpeter initial mass function (IMF) and rules out a bottom light IMF. The different GC subpopulations show markedly distinct orbital distributions at large radii, with red GCs having an anisotropy parameter β ~ 0.4 outside ~ 3Re (Re is the effective radius), and the blue GCs having β ~0.15 at the same radii, while centrally (~1Re) they are both isotropic. We discuss the implications of our findings within the two-phase formation scenario for early-type galaxies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


De Grijs R.,Peking University | Wicker J.E.,CAS National Astronomical Observatories | Bono G.,University of Rome Tor Vergata | Bono G.,National institute for astrophysics
Astronomical Journal | Year: 2014

The distance to the Large Magellanic Cloud (LMC) represents a key local rung of the extragalactic distance ladder yet the galaxy's distance modulus has long been an issue of contention, in particular in view of claims that most newly determined distance moduli cluster tightly - and with a small spread - around the "canonical" distance modulus, (m-M)0 = 18.50 mag. We compiled 233 separate LMC distance determinations published between 1990 and 2013. Our analysis of the individual distance moduli, as well as of their two-year means and standard deviations resulting from this largest data set of LMC distance moduli available to date, focuses specifically on Cepheid and RR Lyrae variable-star tracer populations, as well as on distance estimates based on features in the observational Hertzsprung-Russell diagram. We conclude that strong publication bias is unlikely to have been the main driver of the majority of published LMC distance moduli. However, for a given distance tracer, the body of publications leading to the tightly clustered distances is based on highly non-independent tracer samples and analysis methods, hence leading to significant correlations among the LMC distances reported in subsequent articles. Based on a careful, weighted combination, in a statistical sense, of the main stellar population tracers, we recommend that a slightly adjusted canonical distance modulus of (m-M)0 = 18.49 ± 0.09 mag be used for all practical purposes that require a general distance scale without the need for accuracies of better than a few percent. © 2014. The American Astronomical Society. All rights reserved.


Mason E.,US Space Telescope Science Institute | Williams R.E.,US Space Telescope Science Institute | Della Valle M.,National institute for astrophysics | Setiawan J.,Embassy of the Republic of Indonesia
Astronomy and Astrophysics | Year: 2012

We present optical and near-infrared (NIR) spectroscopic observations of U Sco 2010 outburst. From the analysis of lines profiles we identify a broad and a narrow component and show that the latter originates from the reforming accretion disk. We show that the accretion resumes shortly after the outburst, on day +8, roughly when the super-soft (SSS) X-ray phase starts. Consequently U Sco SSS phase is fueled (in part or fully) by accretion and should not be used to estimate m rem, the mass of accreted material which has not been ejected during the outburst. In addition, most of the He emission lines, and the He ii lies in particular, form in the accretion flow/disk within the binary and are optically thick, thus preventing an accurate abundance determination. A late spectrum taken in quiescence and during eclipse shows Ca ii H&K, the G-band and Mg ib absorption from the secondary star. However, no other significant secondary star features have been observed at longer wavelengths and in the NIR band. © 2012 ESO.


de Almeida U.B.,Brazilian Center for Research in Physics (CBPF) | Tavecchio F.,National institute for astrophysics | Mankuzhiyil N.,University of Trieste | Mankuzhiyil N.,Bhabha Atomic Research Center
Monthly Notices of the Royal Astronomical Society | Year: 2014

In this paper, we propose a way of using optical polarization observations to provide independent constraints and to guide the modelling of the spectral energy distribution (SED) of blazars. This is particularly useful when two-zone models are required to fit the observed SED. As an example, we apply the method to the 2008 multiwavelength campaign of PKS 2155- 304, for which the required polarization information was already available. We find that this approach is able to simultaneously describe the SED and the variability of the source, which is otherwise difficult to interpret. More generally, by using polarization data to disentangle different active regions within the source, the method reveals otherwise unseen correlations in the multiwavelength behaviour, which are important for SED modelling. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Valiante R.,National institute for astrophysics | Schneider R.,National institute for astrophysics | Salvadori S.,University of Groningen | Gallerani S.,Normal School of Pisa
Monthly Notices of the Royal Astronomical Society | Year: 2014

We investigate the evolutionary properties of a sample of quasars (QSOs) at 5 < z < 6.4 using the semi-analytical hierarchical model GAMETE/QSODUST. We find that the observed properties of these QSOs are well reproduced by a common formation scenario in which stars form according to a standard initial mass function, via quiescent star formation and efficient merger-driven bursts, while the central black hole (BH) grows via gas accretion and BH-BH mergers. Eventually, a strong active galactic nuclei-drivenwind starts to clear up the interstellar medium of dust and gas, damping the star formation and un-obscuring the line of sight towards the QSO. In this scenario, all the QSOs hosts have final stellar masses in the range (4-6) × 1011 M⊙, a factor of 3-30 larger than the upper limits allowed by the observations. We discuss alternative scenarios to alleviate this apparent tension: The most likely explanation resides in the large uncertainties that still affect dynamical mass measurements in these high-z galaxies. In addition, during the transition between the starburst-dominated and the active QSO phase, we predict that ~40 per cent of the progenitor galaxies can be classified as Submillimetre Galaxies, although their number rapidly decreases with redshift. © 2014 The Authors.


Cui W.,University of Western Australia | Cui W.,University of Trieste | Borgani S.,University of Trieste | Borgani S.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We investigate baryon effects on the halo mass function (HMF), with emphasis on the role played by active galactic nuclei (AGN) feedback. Haloes are identified with both friends-offriends (FoF) and spherical overdensity (SO) algorithms.We embed the standard SO algorithm into a memory-controlled frame program and present the Python spherIcAl Overdensity code-PIAO (Chinese character: ). For both FoF and SO haloes, the effect of AGN feedback is that of suppressing the HMFs to a level even below that of dark matter (DM) simulations. The ratio between the HMFs in the AGN and in the DM simulations is ∼0.8 at overdensity Δc = 500, a difference that increases at higher overdensity Δc = 2500, with no significant redshift and mass dependence. A decrease of the halo masses ratio with respect to the DM case induces the decrease of the HMF in the AGN simulation. The shallower inner density profiles of haloes in the AGN simulation witnesses that mass reduction is induced by the sudden displacement of gas induced by thermal AGN feedback. We provide fitting functions to describe halo mass variations at different overdensities, which can recover the HMFs with a residual random scatter ≲5 per cent for halo masses larger than 1013 h-1M⊙. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Battaglia G.,Hemisphere | Battaglia G.,National institute for astrophysics | Starkenburg E.,University of Groningen
Astronomy and Astrophysics | Year: 2012

Dwarf galaxies provide insight into the processes of star formation and chemical enrichment at the low end of the galaxy mass function, as well as into the clustering of dark matter on small scales. In studies of Local Group dwarf galaxies, spectroscopic samples of individual stars are used to derive the internal kinematics and abundance properties of these galaxies. It is therefore important to clean these samples from Milky Way stars, which are not related to the dwarf galaxy, since they can contaminate analysis of the properties of these objects. Here we introduce a new diagnostic for separating Milky Way contaminant stars, which mainly consist of dwarf stars, and red giant branch stars targeted in dwarf galaxies. As discriminator we use the trends in the equivalent width of the nIR Mg I line at 8806.8 Å as a function of the equivalent width of Ca II triplet lines. This method is particularly useful for works dealing with multi-object, intermediate-resolution spectroscopy focusing in the region of the nIR Ca II triplet. We use synthetic spectra to explore how the equivalent width of these lines changes for stars with different properties (gravity, effective temperature, metallicity) and find that a distinction among giants above the horizontal branch and dwarfs can be made with this method at [Fe/H] > -2 dex. For -2 ≤ [Fe/H] ≤ -1, this method is also valid for distinguishing dwarfs and giants down to approximately one magnitude below the horizontal branch. Using a foreground model we make predictions on the use of this new discrimination method for nearby dwarf spheroidal galaxies, including the ultra-faints. We subsequently use VLT/FLAMES data for the Sextans, Sculptor, and Fornax dwarf spheroidal galaxies to verify the predicted theoretical trends. © ESO 2012.


De Grijs R.,Peking University | Bono G.,University of Rome Tor Vergata | Bono G.,National institute for astrophysics
Astronomical Journal | Year: 2014

The accuracy of extragalactic distance measurements ultimately depends on robust, high-precision determinations of the distances to the galaxies in the local volume. Following our detailed study addressing possible publication bias in the published distance determinations to the Large Magellanic Cloud (LMC), here we extend our distance range of interest to include published distance moduli to M31 and M33, as well as to a number of their wellknown dwarf galaxy companions. We aim at reaching consensus on the best, most homogeneous, and internally most consistent set of Local Group distance moduli to adopt for future, more general use based on the largest set of distance determinations to individual Local Group galaxies available to date. Based on a careful, statistically weighted combination of the main stellar population tracers (Cepheids, RR Lyrae variables, and the magnitude of the tip of the red-giant branch), we derive a recommended distance modulus to M31 of (m - M) M31 0 = 24.46 ± 0.10 mag - adopting as our calibration an LMC distance modulus of (m - M)LMC 0 = 18.50 mag - and a fully internally consistent set of benchmark distances to key galaxies in the local volume, enabling us to establish a robust and unbiased, near-field extragalactic distance ladder. © 2014. The American Astronomical Society. All rights reserved.


Matteucci F.,University of Trieste | Matteucci F.,National institute for astrophysics | Matteucci F.,National Institute of Nuclear Physics, Italy | Romano D.,National institute for astrophysics | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We have explored the Eu production in the Milky Way by means of a very detailed chemical evolution model. In particular, we have assumed that Eu is formed in merging neutron star (or neutron star-black hole) binaries as well as in Type II supernovae. We have tested the effects of several important parameters influencing the production of Eu during the merging of two neutron stars, such as (i) the time-scale of coalescence, (ii) the Eu yields and (iii) the range of initial masses for the progenitors of the neutron stars. The yields of Eu from Type II supernovae are very uncertain, more than those from coalescing neutron stars, so we have explored several possibilities. We have compared our model results with the observed rate of coalescence of neutron stars, the solar Eu abundance, the [Eu/Fe] versus [Fe/H] relation in the solar vicinity and the [Eu/H] gradient along the Galactic disc. Our main results can be summarized as follows: (i) neutron star mergers can be entirely responsible for the production of Eu in the Galaxy if the coalescence time-scale is no longer than 1Myr for the bulk of binary systems, the Eu yield is around 3 × 10-7 M⊙ and the mass range of progenitors of neutron stars is 9-50M⊙; (ii) both Type II supernovae and merging neutron stars can produce the right amount of Eu if the neutron star mergers produce 2 × 10-7 M⊙ per system and Type II supernovae, with progenitors in the range 20-50M⊙, produce yields of Eu of the order of 10-8-10-9 M⊙; (iii) either models with only neutron stars producing Eu or mixed ones can reproduce the observed Eu abundance gradient along the Galactic disc. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Battaglia G.,National institute for astrophysics | Irwin M.,Institute of Astronomy | Tolstoy E.,University of Groningen | De Boer T.,University of Groningen | Mateo M.,University of Michigan
Astrophysical Journal Letters | Year: 2012

The evolution of small systems such as dwarf spheroidal galaxies (dSphs) is likely to have been a balance between external environmental effects and internal processes within their own relatively shallow potential wells. Assessing how strong such environmental interactions may have been is therefore an important element in understanding the baryonic evolution of dSphs and their derived dark matter distribution. Here we present results from a wide-area CTIO/MOSAIC II photometric survey of the Carina dSph, reaching down to about two magnitudes below the oldest main-sequence turnoff (MSTO). This data set enables us to trace the structure of Carina in detail out to very large distances from its center, and as a function of stellar age. We observe the presence of an extended structure made up primarily of ancient MSTO stars, at distances between 25′ and 60′ from Carina's center, confirming results in the literature that Carina extends well beyond its nominal tidal radius. The large number statistics of our survey reveals features such as isophote twists and tails that were undetected in other previous, shallower surveys. This is the first time that such unambiguous signs of tidal disruption have been found in a Milky Way "classical" dwarf other than Sagittarius. We also demonstrate the presence of a negative age gradient in Carina directly from its MSTOs, and trace it out to very large distances from the galaxy center. The signs of interaction with the Milky Way make it unclear whether the age gradient was already in place before Carina underwent tidal disruption. © 2012. The American Astronomical Society. All rights reserved.


Zhu X.-J.,Beijing Normal University | Fan X.-L.,University of Trieste | Fan X.-L.,National institute for astrophysics | Zhu Z.-H.,Beijing Normal University
Astrophysical Journal | Year: 2011

We revisit the possibility and detectability of a stochastic gravitational wave (GW) background produced by a cosmological population of newborn neutron stars (NSs) with r-mode instabilities. The NS formation rate is derived from both observational and simulated cosmic star formation rates (CSFRs). We show that the resultant GW background is insensitive to the choice of CSFR models, but depends strongly on the evolving behavior of CSFR at low redshifts. Nonlinear effects such as differential rotation, suggested to be an unavoidable feature which greatly influences the saturation amplitude of the r-mode, are considered to account for GW emission from individual sources. Our results show that the dimensionless energy density ΩGW could have a peak amplitude of ≃(1-3.5) × 10-8 in the frequency range (200-1000) Hz, if the smallest amount of differential rotation corresponding to a saturation amplitude of order unity is assumed. However, such a high-mode amplitude is unrealistic as it is known that the maximum value is much smaller and at most 10-2. A realistic estimate of ΩGW should be at least four orders of magnitude lower (∼10-12), which leads to a pessimistic outlook for the detection of the r-mode background. We consider different pairs of terrestrial interferometers (IFOs) and compare two approaches to combine multiple IFOs in order to evaluate the detectability of this GW background. Constraints on the total emitted GW energy associated with this mechanism to produce a detectable stochastic background (a signal-to-noise ratio of 2.56 with 3 year cross-correlation) are ∼10-3 M⊙ 1 c 2 for two co-located advanced LIGO detectors, and 2 × 10-5 M⊙ 1 c 2 for two Einstein telescopes. These constraints may also be applicable to alternative GW emission mechanisms related to oscillations or instabilities in NSs depending on the frequency band where most GWs are emitted. © 2011. The American Astronomical Society. All rights reserved.


Vulcani B.,University of Padua | Vulcani B.,National institute for astrophysics | Poggianti B.M.,National institute for astrophysics | Finn R.A.,Siena College | And 3 more authors.
Astrophysical Journal Letters | Year: 2010

Analyzing 24 μm MIPS/Spitzer data and the [O II]3727 line of a sample of galaxies at 0.4 ≤ z ≤ 0.8 from the ESO Distant Cluster Survey, we investigate the ongoing star formation rate (SFR) and the specific star formation rate (SSFR) as a function of stellar mass in galaxy clusters and groups, and compare these with results from field studies. As for the field, we find a decline in SFR with time, indicating that star formation (SF) was more active in the past, and a decline in SSFR as galaxy stellar mass increases, showing that the current SF contributes more to the fractional growth of low-mass galaxies than high-mass galaxies. However, we find a lower median SFR (by a factor of ∼ 1.5) in cluster star-forming galaxies than in the field. The difference is highly significant when all Spitzer and emission-line galaxies are considered, regardless of color. It remains significant at z > 0.6 after removing red emission-line galaxies, to avoid possible active galactic nucleus contamination. While there is overlap between the cluster and field SFR-mass relations, we find a population of cluster galaxies (10%-25%) with reduced SFR for their mass. These are likely to be in transition from star forming to passive. Separately comparing clusters and groups at z > 0.6, only cluster trends are significantly different from the field, and the average cluster SFR at a given mass is ∼ two times lower than the field. We conclude that the average SFR in star-forming galaxies varies with galaxy environment at a fixed galaxy mass. © 2010. The American Astronomical Society. All rights reserved.


Martel H.,Laval University | Robichaud F.,Laval University | Barai P.,National institute for astrophysics
Astrophysical Journal | Year: 2014

Using a large N-body cosmological simulation combined with a subgrid treatment of galaxy formation, merging, and tidal destruction, we study the formation and evolution of the galaxy and cluster population in a comoving volume (100 Mpc)3 in a ΛCDM universe. At z = 0, our computational volume contains 1788 clusters with mass M cl > 1.1 × 1012 M ⊙, including 18 massive clusters with M cl > 1014 M ⊙. It also contains 1, 088, 797 galaxies with mass M gal ≥ 2 × 109 M ⊙ and luminosity L > 9.5 × 105 L. For each cluster, we identified the brightest cluster galaxy (BCG). We then computed two separate statistics: the fraction f BNC of clusters in which the BCG is not the closest galaxy to the center of the cluster in projection, and the ratio Δv/σ, where Δv is the difference in radial velocity between the BCG and the whole cluster and σ is the radial velocity dispersion of the cluster. We found that f BNC increases from 0.05 for low-mass clusters (M cl ∼ 1012 M ⊙) to 0.5 for high-mass clusters (M cl > 10 14 M ⊙) with very little dependence on cluster redshift. Most of this result turns out to be a projection effect and when we consider three-dimensional distances instead of projected distances, f BNC increases only to 0.2 at high-cluster mass. The values of Δv/σ vary from 0 to 1.8, with median values in the range 0.03-0.15 when considering all clusters, and 0.12-0.31 when considering only massive clusters. These results are consistent with previous observational studies and indicate that the central galaxy paradigm, which states that the BCG should be at rest at the center of the cluster, is usually valid, but exceptions are too common to be ignored. We built merger trees for the 18 most massive clusters in the simulation. Analysis of these trees reveal that 16 of these clusters have experienced 1 or several major or semi-major mergers in the past. These mergers leave each cluster in a non-equilibrium state, but eventually the cluster settles into an equilibrium configuration, unless it is disturbed by another major or semi-major merger. We found evidence that these mergers are responsible for the off-center positions and peculiar velocities of some BCGs. Our results thus support the merging-group scenario, in which some clusters form by the merging of smaller groups in which the galaxies have already formed, including the galaxy destined to become the BCG. Finally, we argue that f BNC is not a very robust statistics, as it is very sensitive to projection and selection effects, but that Δv/σ is more robust. Still, both statistics exhibit a signature of major mergers between clusters of galaxies. © 2014. The American Astronomical Society. All rights reserved.


Salvo C.A.,Ohio State University | Mathur S.,Ohio State University | Ghosh H.,CEA Saclay Nuclear Research Center | Fiore F.,National institute for astrophysics | Ferrarese L.,Hertzberg Institute of Astrophysics
Astrophysical Journal | Year: 2012

We present XMM-Newton observations of the Chandra-detected nuclear X-ray source in NGC4561. The hard X-ray spectrum can be described by a model composed of an absorbed power law with Γ= 2.5+0.4 - 0.3 and column density NH = 1.9+0.1 - 0.2 × 1022 atomscm-2. The absorption-corrected luminosity of the source is L(0.2-10.0keV) =2.5 × 1041ergs-1, with bolometric luminosity over 3 × 1042ergs-1. Based on the spectrum and the luminosity, we identify the nuclear X-ray source in NGC4561 to be an active galactic nucleus (AGN), with a black hole (BH) of mass M BH >2 × 104 M ⊙. The presence of a supermassive black hole at the center of this bulgeless galaxy shows that BH masses are not necessarily related to bulge properties, contrary to general belief. Observations such as these call into question several theoretical models of BH-galaxy coevolution that are based on merger-driven BH growth; secular processes clearly play an important role. Several emission lines are detected in the soft X-ray spectrum of the source which can be well parameterized by an absorbed diffuse thermal plasma with non-solar abundances of some heavy elements. Similar soft X-ray emission is observed in spectra of Seyfert 2 galaxies and low-luminosity AGNs, suggesting an origin in the circumnuclear plasma. © 2012. The American Astronomical Society. All rights reserved.


Mainini R.,National institute for astrophysics | Mota D.F.,University of Oslo
Astrophysical Journal | Year: 2012

We provide an exhaustive analysis of the Integrated Sachs-Wolfe (ISW) effect in the context of coupled dark energy cosmologies where a component of massive neutrinos is also present. We focus on the effects of both the coupling between dark matter and dark energy and of the neutrino mass on the cross-correlation between galaxy/quasar distributions and ISW effect. We provide a simple expression to appropriately rescale the galaxy bias when comparing different cosmologies. Theoretical predictions of the cross-correlation function are then compared with observational data. We find that, while it is not possible to distinguish among the models at low redshifts, discrepancies between coupled models and ΛCDM increase with z. In spite of this, current data alone does not seem able to distinguish between coupled models and ΛCDM. However, we show that upcoming galaxy surveys will permit tomographic analysis that will allow us to better discriminate among the models. We discuss the effects on cross-correlation measurements of ignoring galaxy bias evolution, b(z), and magnification bias correction and provide fitting formulae for b(z) for the cosmologies considered. We compare three different tomographic schemes and investigate how the expected signal-to-noise ratio, S/N, of the ISW-LSS cross-correlation changes when increasing the number of tomographic bins. The dependence of S/N on the area of the survey and the survey shot noise is also discussed.


Bel J.,National institute for astrophysics | Hoffmann K.,Institute Of Ciencies Of Lespai Ice | Gaztanaga E.,Institute Of Ciencies Of Lespai Ice
Monthly Notices of the Royal Astronomical Society | Year: 2015

We study halo clustering bias with second- and third-order statistics of halo and matter density fields in the Marenostrum Institut de Ciències de l'Espai (MICE) Grand Challenge simulation. We verify that two-point correlations deliver reliable estimates of the linear bias parameters at large scales, while estimations from the variance can be significantly affected by nonlinear and possibly non-local contributions to the bias function. Combining three-point autoand cross-correlations we find, for the first time in configuration space, evidence for the presence of such non-local contributions. These contributions are consistent with predicted second-order non-local effects on the bias functions originating from the dark matter tidal field. Samples of massive haloes show indications of bias (local or non-local) beyond second order. Ignoring non-local bias causes 20-30 and 5-10 per cent overestimation of the linear bias from three-point auto- and cross-correlations, respectively. We study two third-order bias estimators that are not affected by second-order non-local contributions. One is a combination of three-point auto- and cross-correlations. The other is a combination of third-order one- and two-point cumulants. Both methods deliver accurate estimations of the linear bias. Ignoring non-local bias causes higher values of the second-order bias from three-point correlations. Our results demonstrate that third-order statistics can be employed for breaking the growth-bias degeneracy. © 2015 The Authors.


Spagna A.,National institute for astrophysics | Lattanzi M.G.,National institute for astrophysics | Re Fiorentin P.,University of Ljubljana | Smart R.L.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

We analyze a new kinematic survey that includes accurate proper motions derived from SDSS DR7 positions, combined with multiepoch measurements from the GSC-II database. By means of the SDSS spectro-photometric data (effective temperature, surface gravity, metallicity, and radial velocities), we estimate photometric parallaxes for a sample of 27 000 FGK (sub)dwarfs with [Fe/H] < -0.5, which we adopted as tracers of the seven-dimensional space distribution (kinematic phase distribution plus chemical abundance) of the thick disk and inner halo within a few kiloparsecs of the Sun. We find evidence of a kinematics-metallicity correlation, ∂ 〈Vφ〉/ ∂[Fe/H] ≈ 40 ÷ 50 km s-1 dex-1, amongst thick disk stars located between one and three kiloparsecs from the plane and with abundance -1 < [Fe/H] < -0.5, while no significant correlation is present for [Fe/H] ≳ -0.5. In addition, we estimate a shallow vertical rotation velocity gradient, ∂ 〈Vφ 〉/∂ |z| = -19 ± 2 km s-1 kpc-1, for the thick disk between 1 kpc < |z| < 3 kpc, and a low prograde rotation, 37 ± 3 km s-1 for the inner halo up to 4 kpc. Finally, we briefly discuss the implications of these findings for the thick disk formation scenarios in the context of CDM hierarchical galaxy formation mechanisms and of secular evolutionary processes in galactic disks. © 2010 ESO.


Martel H.,Laval University | Barai P.,National institute for astrophysics
Astrophysical Journal | Year: 2012

We combine an N-body simulation algorithm with a subgrid treatment of galaxy formation, mergers, and tidal destruction, and an observed conditional luminosity function Φ(L|M), to study the origin and evolution of galactic and extragalactic light inside a cosmological volume of size (100 Mpc) 3, in a concordance ΛCDM model. This algorithm simulates the growth of large-scale structures and the formation of clusters, the evolution of the galaxy population in clusters, the destruction of galaxies by mergers and tides, and the evolution of the intracluster light (ICL). We find that destruction of galaxies by mergers dominates over destruction by tides by about an order of magnitude at all redshifts. However, tidal destruction is sufficient to produce ICL fractions f ICL that are sufficiently high to match observations. Our simulation produces 18 massive clusters (Mcl > 1014 M⊙) with values of fICL ranging from 1% to 58% at z = 0. There is a weak trend of fICL to increase with cluster mass. The bulk of the ICL (∼60%) is provided by intermediate galaxies of total masses 1011-1012 M⊙ and stellar masses 6 × 108 M⊙ to 3 × 10 10 M⊙ that were tidally destroyed by even more massive galaxies. The contribution of low-mass galaxies to the ICL is small and the contribution of dwarf galaxies is negligible, even though, by numbers, most galaxies that are tidally destroyed are dwarfs. Tracking clusters back in time, we find that their values of f ICL tend to increase over time, but can experience sudden changes that are sometimes non-monotonic. These changes occur during major mergers involving clusters of comparable masses but very different intracluster luminosities. Most of the tidal destruction events take place in the central regions of clusters. As a result, the ICL is more centrally concentrated than the galactic light. Our results support tidal destruction of intermediate-mass galaxies as a plausible scenario for the origin of the ICL. © 2012. The American Astronomical Society. All rights reserved.


Villalobos A.,University of Groningen | Villalobos A.,National institute for astrophysics | Kazantzidis S.,Ohio State University | Helmi A.,University of Groningen
Astrophysical Journal | Year: 2010

We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically common 5:1 encounters between initially thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale lengths and scale heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation. © 2010. The American Astronomical Society. All rights reserved.


Blakeslee J.P.,National Research Council Canada | Cantiello M.,National institute for astrophysics | Peng E.W.,Peking University | Peng E.W.,Kavli Institute for Astronomy and Astrophysics
Astrophysical Journal | Year: 2010

Two recent empirical developments in the study of extragalactic globular cluster (GC) populations are the color-magnitude relation of the blue GCs (the "blue tilt") and the nonlinearity of the dependence of optical GC colors on metallicity. The color-magnitude relation, interpreted as a mass-metallicity relation, is thought to be a consequence of self-enrichment. Nonlinear color-metallicity relations have been shown to produce bimodal color distributions from unimodal metallicity distributions. We simulate GC populations including both a mass-metallicity scaling relation and nonlinear color-metallicity relations motivated by theory and observations. Depending on the assumed range of metallicities and the width of the GC luminosity function (GCLF), we find that the simulated populations can have bimodal color distributions with a "blue tilt" similar to observations, even though the metallicity distribution appears unimodal. The models that produce these features have the relatively high mean GC metallicities and nearly equal blue and red peaks characteristic of giant elliptical galaxies. The blue tilt is less apparent in the models with metallicities typical of dwarf ellipticals; the narrower GCLF in these galaxies has an even bigger effect in reducing the significance of their color-magnitude slopes. We critically examine the evidence for nonlinearity versus bimodal metallicities as explanations for the characteristic double-peaked color histograms of giant ellipticals and conclude that the question remains open. We discuss the prospects for further theoretical and observational progress in constraining the models presented here and for uncovering the true metallicity distributions of extragalactic GC systems. © 2010. The American Astronomical Society. All rights reserved..


Lanza A.F.,National institute for astrophysics | Das Chagas M.L.,National institute for astrophysics | Das Chagas M.L.,Grande Rio University | De Medeiros J.R.,Grande Rio University
Astronomy and Astrophysics | Year: 2014

Context. Stellar differential rotation is important for understanding hydromagnetic stellar dynamos, instabilities, and transport processes in stellar interiors, as well as for a better treatment of tides in close binary and star-planet systems. Aims. We introduce a method of measuring a lower limit to the amplitude of surface differential rotation from high-precision, evenly sampled photometric time series, such as those obtained by space-borne telescopes. It is designed to be applied to main-sequence late-type stars whose optical flux modulation is dominated by starspots. Methods. An autocorrelation of the time series was used to select stars that allow an accurate determination of starspot rotation periods. A simple two-spot model was applied together with a Bayesian information criterion to preliminarily select intervals of the time series showing evidence of differential rotation with starspots of almost constant area. Finally, the significance of the differential rotation detection and a measurement of its amplitude and uncertainty were obtained by an a posteriori Bayesian analysis based on a Monte Carlo Markov chain approach. We applied our method to the Sun and eight other stars for which previous spot modelling had been performed to compare our results with previous ones. Results. We find that autocorrelation is a simple method for selecting stars with a coherent rotational signal that is a prerequisite for successfully measuring differential rotation through spot modelling. For a proper Monte Carlo Markov chain analysis, it is necessary to take the strong correlations among different parameters that exist in spot modelling into account. For the planet-hosting star Kepler-30, we derive a lower limit to the relative amplitude of the differential rotation of ΔP/P = 0.0523 ± 0.0016. We confirm that the Sun as a star in the optical passband is not suitable for measuring differential rotation owing to the rapid evolution of its photospheric active regions. In general, our method performs well in comparison to more sophisticated and time-consuming approaches. © 2014 ESO.


Brunetti G.,National institute for astrophysics | Blasi P.,National institute for astrophysics | Reimer O.,University of Innsbruck | Rudnick L.,University of Minnesota | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We combine for the first time all available information about the spectral shape and morphology of the radio halo of the Coma cluster with the recent γ-ray upper limits obtained by the Fermi-Large Area Telescope (LAT) and with the magnetic field strength derived from Faraday rotation measures. We explore the possibility that the radio emission is due to synchrotron emission of secondary electrons. First, we investigate the case of pure secondary models that are merely based on the mechanism of continuous injection of secondary electrons via proton-proton collisions in the intracluster medium. We use the observed spatial distribution of the halo's radio brightness to constrain the amount of cosmic ray protons and their spatial distribution in the cluster that are required by the model. Under the canonical assumption that the spectrum of cosmic rays is a power law in momentum and that the spectrum of secondaries is stationary, we find that the combination of the steep spectrum of cosmic ray protons necessary to explain the spectrum of the halo and the very broad spatial distribution (and large energy density) of cosmic rays result in a γ-ray emission in excess of present limits, unless the cluster magnetic field is relatively large. However, this large magnetic field required to not violate present γ-ray limits appears inconsistent with that derived from recent Faraday rotation measures. Secondly, we investigate more complex models in which the cosmic rays confined diffusively in the Coma cluster and their secondary electrons are all reaccelerated by magnetohydrodynamics turbulence. We show that under these conditions it is possible to explain the radio spectrum and morphology of the radio halo and to predict γ-ray fluxes in agreement with the Fermi-LAT upper limits without tension with present constraints on the cluster magnetic field. Reacceleration of secondary particles also requires a very broad cosmic ray spatial profile, much flatter than that of the intracluster medium, at least provided that both the turbulent and magnetic field energy densities scale with that of the intracluster medium. However, this requirement can be easily alleviated if we assume that a small amount of (additional) seed primary electrons is reaccelerated in the cluster's external regions, or if we adopt flatter scalings of the turbulent and magnetic field energy densities with distance from the cluster centre. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Hoekstra H.,Leiden University | Bartelmann M.,Institute For Theoretische Astrophysik | Dahle H.,University of Oslo | Israel H.,University of Bonn | And 3 more authors.
Space Science Reviews | Year: 2013

Despite consistent progress in numerical simulations, the observable properties of galaxy clusters are difficult to predict ab initio. It is therefore important to compare both theoretical and observational results to a direct measure of the cluster mass. This can be done by measuring the gravitational lensing effects caused by the bending of light by the cluster mass distribution. In this review we discuss how this phenomenon can be used to determine cluster masses and study the mass distribution itself. As sample sizes increase, the accuracy of the weak lensing mass estimates needs to improve accordingly. We discuss the main practical aspects of these measurements. We review a number of applications and highlight some recent results. © 2013 Springer Science+Business Media Dordrecht.


Murase K.,Pennsylvania State University | Murase K.,Institute for Advanced Study | Guetta D.,National institute for astrophysics | Guetta D.,ORT Braude College | Ahlers M.,University of Wisconsin - Madison
Physical Review Letters | Year: 2016

The latest IceCube data suggest that the all-flavor cosmic neutrino flux may be as large as 10-7 GeV cm-2 s-1 sr-1 around 30 TeV. We show that, if sources of the TeV-PeV neutrinos are transparent to γ rays with respect to two-photon annihilation, strong tensions with the isotropic diffuse γ-ray background measured by Fermi are unavoidable, independently of the production mechanism. We further show that, if the IceCube neutrinos have a photohadronic (pγ) origin, the sources are expected to be opaque to 1-100 GeV γ rays. With these general multimessenger arguments, we find that the latest data suggest a population of cosmic-ray accelerators hidden in GeV-TeV γ rays as a neutrino origin. Searches for x-ray and MeV γ-ray counterparts are encouraged, and TeV-PeV neutrinos themselves will serve as special probes of dense source environments. © 2016 American Physical Society.


Meneghetti M.,National institute for astrophysics | Meneghetti M.,National Institute of Nuclear Physics, Italy | Bartelmann M.,ZAH | Dahle H.,University of Oslo | Limousin M.,Aix - Marseille University
Space Science Reviews | Year: 2013

The existence of an arc statistics problem was at the center of a strong debate in the last fifteen years. With the aim to clarify if the optical depth for giant gravitational arcs by galaxy clusters in the so called concordance model is compatible with observations, several studies were carried out which helped to significantly improve our knowledge of strong lensing clusters, unveiling their extremely complex internal structure. In particular, the abundance and the frequency of strong lensing events like gravitational arcs turned out to be a potentially very powerful tool to trace the structure formation. However, given the limited size of observational and theoretical data-sets, the power of arc statistics as a cosmological tool has been only minimally exploited so far. On the other hand, the last years were characterized by significant advancements in the field, and several cluster surveys that are ongoing or planned for the near future seem to have the potential to make arc statistics a competitive cosmological probe. Additionally, recent observations of anomalously large Einstein radii and concentrations in galaxy clusters have reinvigorated the debate on the arc statistics problem. In this paper, we review the work done so far on arc statistics, focussing on what is the lesson we learned and what is likely to improve in the next years. © 2013 Springer Science+Business Media Dordrecht.


Sanna A.,University of Groningen | Mendez M.,University of Groningen | Belloni T.,National institute for astrophysics | Altamirano D.,Sterrenkundig Instituut Anton Pannekoek
Monthly Notices of the Royal Astronomical Society | Year: 2012

We analysed all archival Rossi X-ray Timing Explorer (RXTE) observations of the neutron star low-mass X-ray binary 4U 1636-53 up to 2010 May. In 528 out of 1280 observations we detected kilohertz quasi-periodic oscillations (kHz QPOs), with ~65per cent of these detections corresponding to the so-called lower kHz QPO. Using this QPO we measured, for the first time, the rate at which the QPO frequency changes as a function of QPO frequency. For this we used the spread of the QPO frequency over groups of 10 consecutive measurements, sampling time-scales between 320 and 1600s and the time derivative of the QPO frequency, ν̇ QPO , over time-scales of 32-160s. We found that (i) both the QPO-frequency spread and ν̇ QPO decrease by a factor of ~3 as the QPO frequency increases. (ii) The average value of ν̇ QPO decreases by a factor of ~2 as the time-scale over which the derivative is measured increases from less than 64 to 160s. (iii) The relation between the absolute value of ν̇ QPO and the QPO frequency is consistent with being the same both for the positive and negative QPO-frequency derivatives. We show that, if either the lower or the upper kHz QPO reflects the Keplerian frequency at the inner edge of the accretion disc, these results support a scenario in which the inner part of the accretion disc is truncated at a radius that is set by the combined effect of viscosity and radiation drag. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Belloni T.M.,National institute for astrophysics | Sanna A.,University of Groningen | Mendez M.,University of Groningen
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present the results of the analysis of a large data base of X-ray observations of 22 galactic black hole transients with the Rossi X-Ray Timing Explorer throughout its operative life for a total exposure time of ̃12 ms. We excluded persistent systems and the peculiar source GRS 1915+105, as well as the most recently discovered sources. The semi-automatic homogeneous analysis was aimed at the detection of high-frequency (100-1000 Hz) quasiperiodic oscillations (QPO), of which several cases were previously reported in the literature. After taking into account the number of independent trials, we obtained 11 detections from two sources only: XTE J1550-564 and GRO J1655-40. For the former, the detected frequencies are clustered around 180 and 280 Hz, as previously found. For the latter, the previously reported dichotomy 300-450 Hz is found to be less sharp. We discuss our results in comparison with kHz QPO in neutron-star X-ray binaries and the prospects for future timing X-ray missions. © 2012 The Authors, Monthly Notices of the Royal Astronomical Society.


De Grijs R.,Peking University | Bono G.,University of Rome Tor Vergata | Bono G.,National institute for astrophysics
Astronomical Journal | Year: 2015

Aiming at providing a firm mean distance estimate to the SMC, and thus to place it within the internally consistent Local Group distance framework we recently established, we compiled the current largest database of published distance estimates to the galaxy. Based on careful statistical analysis, we derive mean distance estimates to the SMC using eclipsing binary systems, variable stars, stellar population tracers, and star cluster properties. Their weighted mean leads to a final recommendation for the mean SMC distance of (m- M)0SMC = 18.96 ± 0.02 mag, where the uncertainty represents the formal error. Systematic effects related to lingering uncertainties in extinction corrections, our physical understanding of the stellar tracers used, and the SMC's complex geometry-including its significant line of sight depth, its irregular appearance which renders definition of the galaxy's center uncertain, as well as its high inclination and possibly warped disk-may contribute additional uncertainties possibly exceeding 0.15-0.20 mag. © 2015. The American Astronomical Society. All rights reserved.


Stelzer B.,National institute for astrophysics | Micela G.,National institute for astrophysics | Lopez-Santiago J.,Complutense University of Madrid | Liefke C.,University of Heidelberg
Monthly Notices of the Royal Astronomical Society | Year: 2013

Mdwarfs are the most numerous stars in the Galaxy. They are characterized by strong magnetic activity. The ensuing high-energy emission is crucial for the evolution of their planets and the eventual presence of life on them. We systematically study the X-ray and ultraviolet emission of a subsample of M dwarfs from a recent proper-motion survey, selecting all M dwarfs within 10 pc to obtain a nearly volume-limited sample (~90 per cent completeness). Archival ROSAT, XMM-Newton andGALEX data are combined with published spectroscopic studies of Hα emission and rotation to obtain a broad picture of stellar activity on M dwarfs. We make use of synthetic model spectra to determine the relative contributions of photospheric and chromospheric emission to the ultraviolet flux. We also analyse the same diagnostics for a comparison sample of young Mdwarfs in the TWHya association (~10 Myr). We find that generally the emission in the GALEX bands is dominated by the chromosphere but the photospheric component is not negligible in early-M field dwarfs. The surface fluxes for the Ha, near-ultraviolet, far-ultraviolet and X-ray emission are connected via a power-law dependence. We present here for the first time such flux-flux relations involving broad-band ultraviolet emission for M dwarfs. Activity indices are defined as flux ratio between the activity diagnostic and the bolometric flux of the star in analogy to the Ca II RHK index. For given spectral type, these indices display a spread of 2-3 dex which is largest for M4 stars. Strikingly, at mid-M spectral types, the spread of rotation rates is also at its highest level. The mean activity index for fast rotators, likely representing the saturation level, decreases from X-rays over the FUV to the NUV band and Hα, i.e. the fractional radiation output increases with atmospheric height. The comparison to the ultraviolet and X-ray properties of TWHya members shows a drop of nearly three orders of magnitude for the luminosity in these bands between ~10 Myr and fewGyr age. A few young field dwarfs (<1Gyr) in the 10-pc sample bridge the gap indicating that the drop in magnetic activity with age is a continuous process. The slope of the age decay is steeper for the X-ray than for the UV luminosity. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ellison S.L.,University of Victoria | Nair P.,National institute for astrophysics | Patton D.R.,Trent University | Scudder J.M.,University of Victoria | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

The star formation rates (SFRs) and metallicities of a sample of 294 galaxies with visually classified, strong, large-scale bars are compared to a control sample of unbarred disc galaxies selected from the Sloan Digital Sky Survey Data Release 4. The fibre (inner few kpc) metallicities of barred galaxies are uniformly higher (at a given mass) than the unbarred sample by ~0.06 dex. However, the fibre SFRs of the visually classified barred galaxies are higher by about 60 per cent only in the galaxies with total stellar mass M {black star} > 10 10 M ⊙. The metal enhancement at M {black star} < 10 10 M ⊙ without an accompanying increase in the SFR may be due to a short-lived phase of early bar-triggered star formation in the past, compared to on-going SFR enhancements in higher mass barred galaxies. There is no correlation between bar length or bar axial ratio with the enhancement of the SFR. In order to assess the relative importance of star formation triggered by bars and galaxy-galaxy interactions, SFRs are also determined for a sample of close galaxy pairs. Both mechanisms appear to be similarly effective at triggering central star formation for galaxies with M {black star} > 10 10 M ⊙. However, due to the much lower fraction of pairs than bars, bars account for ~3.5 times more triggered central star formation than interactions. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Cardone V.F.,National institute for astrophysics | Cardone V.F.,University of Naples Federico II | Leubner M.P.,University of Innsbruck | del Popolo A.,University of Catania
Monthly Notices of the Royal Astronomical Society | Year: 2011

The consideration of galaxies as self-gravitating systems of many collisionless particles allows us to use methods of statistical mechanics for inferring the distribution function of these stellar systems. Actually, the long-range nature of the gravitational force contrasts with the underlying assumptions of Boltzmann statistics, where the interactions among particles are assumed to be short-ranged. A particular generalization of the classical Boltzmann formalism is available within the non-extensive context of Tsallisq-statistics, subject to the non-additivity of the entropies of subsystems. Assuming stationarity and isotropy in the velocity space, when solving the generalized collisionless Boltzmann equation it is possible to derive the galaxy distribution function and density profile. We present a particular set of non-extensive models and we investigate their dynamical and observable properties. As a test of the viability of this generalized context, we fit the rotation curve of M33, showing that the proposed approach leads to dark matter haloes in excellent agreement with the observed data. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Mendez M.,University of Groningen | Altamirano D.,University of Amsterdam | Belloni T.,National institute for astrophysics | Sanna A.,University of Cagliari
Monthly Notices of the Royal Astronomical Society | Year: 2013

We measured the phase-lag spectrum of the high-frequency quasi-periodic oscillations (QPO) in the black hole systems (at QPO frequencies) GRS 1915+105 (35Hz and 67 Hz), GRO J1655-40 (300 Hz and 450 Hz), XTE J1550-564 (180 Hz and 280 Hz) and IGR J17091-3624 (67 Hz). The lag spectra of the 67-Hz QPOin, respectively, GRS 1915+105 and IGR J17091-3624, and the 450-Hz QPO in GRO J1655-40 are hard (hard photons lag the soft ones) and consistent with each other, with the hard lags increasing with energy. On the contrary, the lags of the 35- Hz QPO in GRS 1915+105 are soft, with the lags becoming softer as the energy increases; the lag spectrum of the 35-Hz QPO is inconsistent with that of the 67-Hz QPO. The lags of the 300-Hz QPO in GRO J1655-40, and the 180-Hz and the 280-Hz QPO in XTE J1550-564 are independent of energy, consistent with each other and with being zero or slightly positive (hard lags). For GRO J1655-40, the lag spectrum of the 300-Hz QPO differs significantly from that of the 450-Hz QPOs. The similarity of the lag spectra of the 180-Hz and 280-Hz QPO in XTE J1550-564 suggests that these two are the same QPO seen at a different frequency in different observations. If this is correct, the lags could provide an alternative way to identify the high-frequency QPO features in galactic black hole systems. The lag spectrum of the 67-Hz QPO in GRS 1915+105 (hard lags) is significantly different from that of the 2.7 × 10-4 Hz QPO in the narrow-line Seyfert 1 galaxy RE J1034+396 (soft lags), which disproves the suggestion that the two QPOs are the same physical phenomenon with their frequencies scaled only by the black hole mass. The lag spectrum of the QPO in RE J1034+396 is similar to that of the 35-Hz QPO in GRS 1915+105, although identifying these two QPOs as being the same physical feature remains problematic. We compare our results with those for the lags of the kilohertz QPOs in neutron-star systems and the broad-band noise component in active galactic nuclei, and discuss possible scenarios for producing the lags in these systems. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Wang L.,CAS National Astronomical Observatories | Weinmann Simone M. S.M.,Leiden University | De Lucia Gabriella G.,National institute for astrophysics | Yang Xiaohu X.,Shanghai JiaoTong University | Yang Xiaohu X.,Shanghai Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013

Assembly bias describes the finding that the clustering of dark matter haloes depends on halo formation time at fixed halo mass. In this paper, we analyse the influence of assembly bias on galaxy clustering using both semi-analytic galaxy formation models (SAMs) and observational data. At fixed stellar mass, SAMs predict that the clustering of central galaxies depends on the specific star formation rate (sSFR), with more passive galaxies having a higher clustering amplitude. We find similar trends using the Sloan Digital Sky Survey (SDSS) group catalogues, and verify that these are not affected by possible biases due to the group finding algorithm. Low-mass central galaxies reside in narrow bins of halo mass, so the observed trends of higher clustering amplitude for galaxies with lower sSFR is not driven by variations of the parent halo mass. We argue that the clustering dependence on sSFR represent a direct detection of assembly bias. In addition, contrary to what expected based on clustering of dark matter haloes, we find that low-mass central galaxies in SAMs with larger host halo mass have a lower clustering amplitude than their counter-parts residing in lower mass haloes. This results from the fact that, at fixed stellar mass, assembly bias has a stronger influence on clustering than the dependence on the parent halo mass. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Hinkle K.H.,U.S. National Optical Astronomy Observatories | Wallace L.,U.S. National Optical Astronomy Observatories | Ram R.S.,University of York | Bernath P.F.,University of York | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

Using laboratory hollow cathode spectra we have identified lines of the less common magnesium isotopologues of MgH, 25MgH and 26MgH, in the A 2Π-X 2Σ+ system. Based on the previous analysis of 24MgH, molecular lines have been measured and molecular constants derived for 25MgH and 26MgH. Term values and linelists, in both wavenumber and wavelength units, are presented. The A 2Π-X 2Σ+ system of MgH is important for measuring the magnesium isotope ratios in stars. Examples of analysis using the new linelists to derive the Mg isotope ratio in a metal poor dwarf and giant are shown. © 2013. The American Astronomical Society. All rights reserved.


Noel N.E.D.,ETH Zurich | Noel N.E.D.,University of Surrey | Greggio L.,National institute for astrophysics | Renzini A.,National institute for astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2013

Stellar population models are commonly calculated using star clusters as calibrators for those evolutionary stages that depend on free parameters. However, discrepancies exist among different models, even if similar sets of calibration clusters are used. With the aim of understanding these discrepancies, and of improving the calibration procedure, we consider a set of 43 Magellanic Cloud (MC) clusters, taking age and photometric information from the literature. We carefully assign ages to each cluster based on up-to-date determinations, ensuring that these are as homogeneous as possible. To cope with statistical fluctuations, we stack the clusters in five age bins, deriving for each of them integrated luminosities and colors. We find that clusters become abruptly red in optical and optical-infrared colors as they age from 0.6 to 1 Gyr, which we interpret as due to the development of a well-populated thermally pulsing asymptotic giant branch (TP-AGB). We argue that other studies missed this detection because of coarser age binnings. Maraston and Girardi et al. models predict the presence of a populated TP-AGB at 0.6 Gyr, with a correspondingly very red integrated color, at variance with the data; Bruzual & Charlot and Conroy models run within the error bars at all ages. The discrepancy between the synthetic colors of Maraston models and the average colors of MC clusters results from the now obsolete age scale adopted. Finally, our finding that the TP-AGB phase appears to develop between 0.6 and 1 Gyr is dependent on the adopted age scale for the clusters and may have important implications for stellar evolution. © 2013. The American Astronomical Society. All rights reserved.


Guandalini R.,University of Hertfordshire | Guandalini R.,University of Perugia | Cristallo S.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2013

Context. Stars evolving along the asymptotic giant branch can become carbon-rich in the final part of their evolution. They replenish the inter-stellar medium with nuclear processed material via strong radiative stellar winds. The determination of the luminosity function of these stars, even if far from being conclusive, is extremely important for testing the reliability of theoretical models. In particular, strong constraints on the mixing treatment and the mass-loss rate can be derived. Aims. We present an updated luminosity function of Galactic carbon stars (LFGCS) obtained from a re-analysis of available data already published in previous papers. Methods. Starting from available near-and mid-infrared photometric data, we re-determined the selection criteria. Moreover, we took advantage of updated distance estimates and period-luminosity relations and we adopted a new formulation for the computation of bolometric corrections (BCs). This led us to collect an improved sample of carbon-rich sources from which we constructed an updated luminosity function. Results. The LFGCS peaks at magnitudes around-4.9, confirming the results obtained in a previous work. Nevertheless, the luminosity function presents two symmetrical tails instead of the larger high-luminosity tail characterizing the former luminosity function. Conclusions. The derived LFCGS matches the indications from recent theoretical evolutionary asymptotic giant branch models, thus confirming the validity of the choices of mixing treatment and mass-loss history. Moreover, we compare our new luminosity function with its counterpart in the Large Magellanic Cloud finding that the two distributions are very similar for dust-enshrouded sources, as expected from stellar evolutionary models. Finally, we derive a new fitting formula aimed to better determine BCs for C-stars. © 2013 ESO.


Mucciarelli A.,University of Bologna | Pancino E.,National institute for astrophysics | Pancino E.,Science Data Center | Lovisi L.,University of Bologna | And 2 more authors.
Astrophysical Journal | Year: 2013

GALA is a freely distributed Fortran code for automatically deriving the atmospheric parameters (temperature, gravity, microturbulent velocity, and overall metallicity) and abundances for individual species of stellar spectra using the classical method based on the equivalent widths of metallic lines. The abundances of individual spectral lines are derived by using the WIDTH9 code developed by R. L. Kurucz. GALA is designed to obtain the best model atmosphere by optimizing temperature, surface gravity, microturbulent velocity, and metallicity after rejecting the discrepant lines. Finally, it computes accurate internal errors for each atmospheric parameter and abundance. GALA is suitable for analyzing both early- and late-type stars, under the assumption of local thermodynamical equilibrium. The code permits us to obtain chemical abundances and atmospheric parameters for large stellar samples in a very short time, thus making GALA a useful tool in the epoch of multi-object spectrographs and large surveys. An extensive set of tests with both synthetic and observed spectra is performed and discussed to explore the capabilities and robustness of the code. © 2013. The American Astronomical Society. All rights reserved..


Li Y.-S.,University of Groningen | De Lucia G.,National institute for astrophysics | Helmi A.,University of Groningen
Monthly Notices of the Royal Astronomical Society | Year: 2010

We combine a series of high-resolution simulations with semi-analytical galaxy formation models to follow the evolution of a system resembling the Milky Way and its satellites. The semi-analytical model is based on that developed for the Millennium Simulation, and successfully reproduces the properties of galaxies on large scales as well as those of the Milky Way. In this model, we are able to reproduce the luminosity function of the satellites around the Milky Way by preventing cooling in haloes with Vvir < 16.7 km s -1 (i.e. the atomic hydrogen cooling limit) and including the impact of the reionization of the Universe. The physical properties of our model satellites (e.g. mean metallicities, ages, half-light radii and mass-to-light ratios) are in good agreement with the latest observational measurements. We do not find a strong dependence upon the particular implementation of supernova feedback, but a scheme which is more efficient in galaxies embedded in smaller haloes, i.e. shallower potential wells, gives better agreement with the properties of the ultrafaint satellites. Our model predicts that the brightest satellites are associated with the most massive subhaloes, are accreted later (z ≲ 1) and have extended star formation histories, with only 1 per cent of their stars made by the end of the reionization. On the other hand, the fainter satellites tend to be accreted early and are dominated by stars with age >10 Gyr, and a few of them formed most of their stars before the reionization was complete. Objects with luminosities comparable to those of the classical MW satellites are associated with dark matter subhaloes with a peak circular velocity ≳10 km s-1, in agreement with the latest constraints. © 2009 RAS.


D'elia V.,National institute for astrophysics | Stratta G.,Science Data Center
Astronomy and Astrophysics | Year: 2011

Context. Dark gamma-ray bursts (GRBs) are sources with no or faint optical/near infrared (NIR) afterglow with respect to the X-ray one. Three possible explanations of this optical darkness have been proposed, namely: i) the GRB might be at high redshift, such that the Lyman α absorption prevents optical identifications; ii) dust in the GRB host galaxy may absorb the optical/NIR wavelengths; and iii) the optical faintness might have an intrinsic origin. Aims. We study two dark GRBs discovered by Swift, namely, GRB 100614A and GRB 100615A. These sources are bright in the X-rays, but no optical/NIR afterglow has been detected for either source, despite the efforts of several follow-up campaigns that have been performed since soon after the GRB explosion. Methods. We analyze the X-ray data and collect all the optical/NIR upper limits in literature for these bursts. We then build optical-to-X-ray spectral energy distributions (SEDs) at the times at which the reddest upper limits are available, and we model our SEDs with the attenuation curves of the Milky Way (MW), Small Magellanic Cloud (SMC), and one obtained for a sample of starburst galaxies. Results. We find that to explain the deepest NIR upper limits assuming either a MW or SMC extinction law, the visual extinction towards GRB 100614A is AV > 47 mag, while for GRB 100615A we obtain AV > 58 mag using data taken within one day after the burst and AV > 22 mag even 9.2 days after the trigger. Conclusions. If these bursts were strongly extincted by dust, these results imply that a MW or SMC-like dust obscuration is unlikely to be able to explain their optical darkness. Since both GRBs are bright in X-rays, explanation iii) also cannot explain their dark classification, unless optical radiation and X-rays are not part of the same synchrotron spectrum. In particular, the X-ray emission during the first 100-10 000 s after the burst, shows in ~70% of the cases a "shallow phase" unexpected by the fireball model, typically not tracked at optical wavelengths, that could mimic a stronger optical dust extinction than the real one. An alternative, or complementary explanation of the previous possibility, involves greyer extinction laws. A starburst attenuation curve gives AV > 11 (AV > 15) for GRB 100614A (GRB 100615A) before 1 day after the burst, which is less extreme, despite still very high. Assuming high redshift in addition to extinction, implies that AV > 10 at z = 2 and A V > 4-5 at z = 5, regardless of the adopted extinction recipe. These lower limits are well above the AV computed for previous GRBs at known redshift, but not unlikely. A different, exotic possibility would be an extremely high redshift origin (z > 17 given the missing K detections). Population III stars are expected to emerge at z ~ 20 and can produce GRBs with energies well above those inferred for our GRBs at these redshifts. However, high NH values (above the Galactic ones) toward our GRBs challenge this scenario. Mid-and far-IR late afterglow (>105 s after trigger) observations of these extreme class of GRBs can help us to differentiate between the proposed scenarios. © 2011 ESO.


Munari E.,University of Trieste | Munari E.,National institute for astrophysics | Biviano A.,National institute for astrophysics | Borgani S.,University of Trieste | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present an analysis of the relation between the masses of cluster- and group-sized haloes, extracted from Λ cold dark matter (ΛCDM) cosmological N-body and hydrodynamic simulations, and their velocity dispersion at different redshifts from z = 2 to 0. The main aim of this analysis is to understand how the implementation of baryonic physics in simulations affects such relations, i.e. to what extent the use of the velocity dispersion as a proxy for cluster mass determination is hampered by the imperfect knowledge of the baryonic physics. In our analysis, we use several sets of simulations with different physics implemented: one DM-only simulation, one simulation with non-radiative gas, and two radiative simulations, one of which with feedback from active galactic nuclei. Velocity dispersions are determined using three different tracers: DM particles, subhaloes and galaxies. We confirm that DM particles trace a relation that is fully consistent with the theoretical expectations based on the virial theorem, σv ∝ Mαwith α = 1/3, and with previous results presented in the literature. On the other hand, subhaloes and galaxies trace steeper relations, with velocity dispersion scaling with mass with α > 1/3, and with larger values of the normalization. Such relations imply that galaxies and subhaloes have a ∼10 per cent velocity bias relative to the DM particles, which can be either positive or negative, depending on the halo mass, redshift and physics implemented in the simulation. We explain these differences as due to dynamical processes, namely dynamical friction and tidal disruption, acting on substructures and galaxies, but not on DM particles. These processes appear to be more or less effective, depending on the halo masses and the importance of baryon cooling, and may create a non-trivial dependence of the velocity bias and the σ ID-M200 relation on the tracer, the halo mass and its redshift. These results are relevant in view of the application of velocity dispersion as a proxy for cluster masses in ongoing and future large redshift surveys. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Romano D.,National institute for astrophysics | Starkenburg E.,University of Victoria
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present a new approach for chemical evolution modelling, specifically designed to investigate the chemical properties of dwarf galaxies in a full cosmological framework. In particular, we focus on the Sculptor dwarf spheroidal galaxy, for which a wealth of observational data exists, as a test bed for our model. We select four candidate Sculptor-like galaxies from the satellite galaxy catalogue generated by implementation of a version of the Munich semianalytic model for galaxy formation on the level 2 Aquarius dark matter simulations and use the mass assembly and star formation histories predicted for these four systems as an input for the chemical evolution code. We follow explicitly the evolution of several chemical elements, both in the cold gas out of which the stars form and in the hot medium residing in the halo. We take into account in detail the lifetimes of stars of different initial masses, the distribution of the delay times for Type Ia supernova explosions and the dependence of the stellar yields from the initial metallicity of the stars. We allow large fractions of metals to be deposited into the hot phase, either directly as stars die or through reheated gas flows powered by supernova explosions. We find that, in order to reproduce both the observed metallicity distribution function and the observed abundance ratios of long-lived stars of Sculptor, large fractions of the reheated metals must never re-enter regions of active star formation. With this prescription, all the four analogues to the Sculptor dwarf spheroidal galaxy extracted from the simulated satellites catalogue on the basis of luminosity and stellar population ages are found to reasonably match the detailed chemical properties of real Sculptor stars. However, all model galaxies do severely underestimate the fraction of very metal poor stars observed in Sculptor. Our analysis thus sets further constraints on the semi-analytical models and, at large, on possible metal enrichment scenarios for the Sculptor dwarf spheroidal galaxy. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bianconi M.,University of Innsbruck | Ettori S.,National institute for astrophysics | Ettori S.,National Institute of Nuclear Physics, Italy | Nipoti C.,University of Bologna
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study simple models of massive galaxy clusters in which the intracluster medium (ICM) rotates differentially in equilibrium in the cluster gravitational potential. We obtain the X-ray surface-brightness maps, evaluating the isophote flattening due to the gas rotation. Using a set of different rotation laws, we put constraint on the amplitude of the rotation velocity, finding that rotation curves with peak velocity up to ~600 km s-1 are consistent with the ellipticity profiles of observed clusters. We convolve each of our models with the instrument response of the X-ray Calorimeter Spectrometer on board the ASTRO-H to calculate the simulated X-ray spectra at different distance from the X-ray centre. We demonstrate that such an instrument will allow us to measure rotation of the ICM in massive clusters, even with rotation velocities as low as ~100 km s-1. ©2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Susino R.,National institute for astrophysics | Bemporad A.,National institute for astrophysics | Krucker S.,University of Applied Sciences and Arts Northwestern Switzerland | Krucker S.,University of California at Berkeley
Astrophysical Journal | Year: 2013

Off-limb observations of the solar corona after coronal mass ejections (CMEs) often show strong, compact, and persistent UV sources behind the eruption. They are primarily observed by the SOHO/UVCS instrument in the "hot" [Fe XVIII] λ974 line and are usually interpreted as a signature of plasma heating due to magnetic reconnection in the post-CME current sheet (CS). Nevertheless, the physical process itself and the altitude of the main energy release are currently not fully understood. In this work, we study the evolution of plasma heating after the CME of 2004 July 28 by comparing UV spectra acquired by UVCS with soft and hard X-ray (SXR, HXR) images of the post-flare loops taken by GOES/SXI and RHESSI. The X-ray data show a long-lasting extended source that is rising upward, toward the high-temperature source detected by UVCS. UVCS data show the presence of significant non-thermal broadening in the CS (a signature of turbulent motions) and a strong density gradient across the CS region. The thermal energy released in the HXR source is on the order of ∼1032 erg, a factor ∼2-5 larger than the energy required to explain the high-temperature plasma sampled by UVCS. Nevertheless, the very different time evolutions of SXR and HXR sources compared with the UV emission suggest that reconnection occurring above the post-eruption arcades is not directly responsible for the high-temperature plasma sampled higher up by UVCS. We conclude that an additional plasma heating mechanism (such as turbulent reconnection) in the CS is likely required. © 2013. The American Astronomical Society. All rights reserved..


Caprioli D.,National institute for astrophysics | Caprioli D.,Kavli Institute for Theoretical Physics | Amato E.,National institute for astrophysics | Amato E.,Kavli Institute for Theoretical Physics | And 2 more authors.
Astroparticle Physics | Year: 2010

The supernova paradigm for the origin of galactic cosmic rays has been deeply affected by the development of the non-linear theory of particle acceleration at shock waves. Here we discuss the implications of applying such theory to the calculation of the spectrum of cosmic rays at Earth as accelerated in supernova remnants and propagating in the Galaxy. The spectrum is calculated taking into account the dynamical reaction of the accelerated particles on the shock, the generation of magnetic turbulence which enhances the scattering near the shock, and the dynamical reaction of the amplified field on the plasma. Most important, the spectrum of cosmic rays at Earth is calculated taking into account the flux of particles escaping from upstream during the Sedov-Taylor phase and the adiabatically decompressed particles confined in the expanding shell and escaping at later times. We show how the spectrum obtained in this way is well described by a power law in momentum with spectral index close to -4, despite the concave shape of the instantaneous spectra of accelerated particles. On the other hand we also show how the shape of the spectrum is sensible to details of the acceleration process and environment which are and will probably remain very poorly known. © 2010 Elsevier B.V. All rights reserved.


Barbera F.L.,National institute for astrophysics | Ferreras I.,University College London | Vazdekis A.,Institute of Astrophysics of Canarias | Vazdekis A.,University of La Laguna
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2015

The initial mass function (IMF) of early-type galaxies (ETGs) has been found to feature systematic variations by both dynamical and spectroscopic studies. In particular, spectral line strengths, based on gravity-sensitive features, suggest an excess of low-mass stars in massive ETGs, i.e. a bottom-heavy IMF. The physical drivers of IMF variations are currently unknown. The abundance ratio of α elements, such as [Mg/Fe], has been suggested as a possible driver of the IMF changes, although dynamical constraints do not support this claim. In this letter, we take advantage of the large Sloan Digital Sky Survey data base. Our sample comprises 24 781 high-quality spectra, covering a large range in velocity dispersion (100 < σ0 < 320 km s-1) and abundance ratio (-0.1 < [Mg/Fe] < +0.4). The large volume of data allows us to stack the spectra at fixed values of σ0 and [Mg/Fe]. Our analysis - based on gravity-sensitive line strengths - gives a strong correlation with central velocity dispersion and a negligible variationwith [Mg/Fe] at fixed σ0. This result is robust against individual elemental abundance variations, and seems not to raise any apparent inconsistency with the alternativemethod based on galaxy dynamics. © 2015 The Authors.


Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics | Gheller C.,CSCS | Bruggen M.,Hamburger Sternwarte
Monthly Notices of the Royal Astronomical Society | Year: 2014

Non-thermal (relativistic) particles are injected into the cosmos by structure formation shock waves, active galactic nuclei and stellar explosions. We present a suite of unigrid cosmological simulations (up to 20483) using a two-fluid model in the grid code ENZO. The simulations include the dynamical effects of cosmic ray (CR) protons and cover a range of theoretically motivated acceleration efficiencies. For the bulk of the cosmic volume the modelling of CR processes is rather stable with respect to resolution, provided that a minimum (cell) resolution of̃100 kpc h-1 is employed. However, the results for the innermost cluster regions depend on the assumptions for the baryonic physics. Inside clusters, non-radiative runs at high resolution tend to produce an energy density of CRs that are below available upper limits from the Fermi satellite, while the radiative runs are found to produce a higher budget of CRs. We show that weak (M ≤ 3-5) shocks and shock-re-acceleration are crucial to set the level of CRs in the innermost region of clusters, while in the outer regions the level of CR energy is mainly set via direct injection by stronger shocks, and is less sensitive to cooling and feedback from active galactic nuclei and supernovae. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Tissera P.B.,CONICET | Tissera P.B.,Institute Astronomia y Fisica del Espacio | Tissera P.B.,Andrés Bello University | Beers T.C.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a comprehensive study of the chemical properties of the stellar haloes of Milky Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ̃15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighbourhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01] dex kpc-1. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics | Bruggen M.,Hamburger Sternwarte | Gheller C.,CSCS | Wang P.,NVDIA
Monthly Notices of the Royal Astronomical Society | Year: 2014

The amplification of primordial magnetic fields via a small-scale turbulent dynamo during structure formation might be able to explain the observed magnetic fields in galaxy clusters. The magnetization of more tenuous large-scale structures such as cosmic filaments is more uncertain, as it is challenging for numerical simulations to achieve the required dynamical range. In this work, we present magnetohydrodynamical cosmological simulations on large uniform grids to study the amplification of primordial seed fields in the intracluster medium (ICM) and in the warm-hot-intergalactic medium (WHIM). In the ICM, we confirm that turbulence caused by structure formation can produce a significant dynamo amplification, even if the amplification is smaller than what is reported in other papers. In the WHIM inside filaments, we do not observe significant dynamo amplification, even though we achieve Reynolds numbers of Re ~ 200-300. The maximal amplification for large filaments is of the order of ~100 for the magnetic energy, corresponding to a typical field of a few ~nG starting from a primordial weak field of 10-10 G (comoving). In order to start a small-scale dynamo, we found that a minimum of ~102 resolution elements across the virial radius of galaxy clusters was necessary. In filaments we could not find a minimum resolution to set off a dynamo. This stems from the inefficiency of supersonic motions in the WHIM in triggering solenoidal modes and small-scale twisting of magnetic field structures. Magnetic fields this small will make it hard to detect filaments in radio observations. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Modica P.,University Paris - Sud | Modica P.,National institute for astrophysics | Palumbo M.E.,National institute for astrophysics | Strazzulla G.,National institute for astrophysics
Planetary and Space Science | Year: 2012

Methyl formate is a complex organic molecule considered potentially relevant as precursor of biologically active molecules. It has been observed in several astrophysical environments, such as hot cores, hot corinos, and comets. The processes that drive the formation of molecules in cometary ices are poorly understood. In particular it is not yet clear if molecules are directly accreted from the pre-solar nebula to form comets or are formed after accretion. The present work analyzes the possible role of cosmic ion irradiation and radioactive decay in methyl formate formation in methanol-bearing ices. The results indicate that cosmic ion irradiation can account for about 12% of the methyl formate observed in comet Hale-Bopp, while radioactive decay can account for about 6% of this amount. The need of new data coming from earth based and space observational projects as well as from laboratory experiments is outlined. © 2012 Elsevier Ltd. All rights reserved.


Vazza F.,Hamburger Sternwarte | Vazza F.,National institute for astrophysics | Bruggen M.,Hamburger Sternwarte
Monthly Notices of the Royal Astronomical Society | Year: 2014

Radio relics in galaxy clusters are thought to be associated with powerful shock waves that accelerate particles via diffusive shock acceleration (DSA). Among the particles accelerated by DSA, relativistic protons should outnumber electrons by a large factor.While the relativistic electrons emit synchrotron emission detectable in the radio band, the protons interact with the thermal gas to produce gamma-rays in hadronic interactions. Using simple models for the propagation of shock waves through clusters, the distribution of thermal gas and the efficiency of DSA, we find that the resulting hadronic gamma-ray emission lies very close or above the upper limits from the Fermi data on nearby clusters. This suggests that the relative acceleration efficiency of electrons and protons is at odds with predictions from DSA. The inclusion of re-accelerated 'fossil' particles does not seem to solve the problem. Our study highlights a possible tension of the commonly assumed scenario for the formation of radio relics and we discuss possible solutions to the problem. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


He J.-H.,National institute for astrophysics | Wang B.,Shanghai JiaoTong University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We reconstruct an f(R) gravity model that gives rise to the particular ΛCDM background evolution of the Universe. We find well-defined, real-valued analytical forms for the f(R) model to describe the Universe both in the early epoch from the radiation to matter dominated eras and the late time acceleration period. We further examine the viability of the derived f(R) model and find that it is viable to describe the evolution of the Universe in the past and the future singularity does not exist in the Lagrangian. © 2013 American Physical Society.


He J.-H.,National institute for astrophysics | Li B.,Durham University | Jing Y.P.,Shanghai JiaoTong University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In this paper, we study the nonlinear matter power spectrum in a specific family of f(R) models that can reproduce the ΛCDM background expansion history, using high resolution N-body simulations based on the ecosmog code. We measure the matter power spectrum in the range of 0.05h Mpc-1 < k<10h Mpc-1 from simulations for our f(R) models and give theoretical explanations to their behavior and evolution patterns. We also examine the chameleon mechanism for our models and find that it works throughout the cosmic history in dense regions, for our f(R) models with |f R0|<10-4. On the other hand, for models with |f R0|>10-3, we find no chameleon screening in dense regions at late times (z<3), which means that those models could be ruled out due to the factor-of-1/3 enhancement to the strength of Newtonian gravity. We also give the best-fit parameters for a generalized parametrized post-Friedman fitting formula, which works well for the models studied here. © 2013 American Physical Society.


Bisterzo S.,National institute for astrophysics | Bisterzo S.,University of Turin | Travaglio C.,National institute for astrophysics | Gallino R.,University of Turin | And 2 more authors.
Astrophysical Journal | Year: 2014

We study the s-process abundances (A ≳ 90) at the epoch of the solar system formation. Asymptotic giant branch yields are computed with an updated neutron capture network and updated initial solar abundances. We confirm our previous results obtained with a Galactic chemical evolution (GCE) model: (1) as suggested by the s-process spread observed in disk stars and in presolar meteoritic SiC grains, a weighted average of s-process strengths is needed to reproduce the solar s distribution of isotopes with A > 130; and (2) an additional contribution (of about 25%) is required in order to represent the solar s-process abundances of isotopes from A = 90 to 130. Furthermore, we investigate the effect of different internal structures of the 13C pocket, which may affect the efficiency of the 13C(α, n) 16O reaction, the major neutron source of the s process. First, keeping the same 13C profile adopted so far, we modify by a factor of two the mass involved in the pocket; second, we assume a flat 13C profile in the pocket, and we test again the effects of the variation of the mass of the pocket. We find that GCE s predictions at the epoch of the solar system formation marginally depend on the size and shape of the 13C pocket once a different weighted range of 13C-pocket strengths is assumed. We obtain that, independently of the internal structure of the 13C pocket, the missing solar system s-process contribution in the range from A = 90 to 130 remains essentially the same. © 2014. The American Astronomical Society. All rights reserved.


Coffey D.,Dublin Institute for Advanced Studies | Coffey D.,National institute for astrophysics | Rigliaco E.,National institute for astrophysics | Bacciotti F.,National institute for astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2012

We present results of the second phase of our near-ultraviolet investigation into protostellar jet rotation using the Hubble Space Telescope Imaging Spectrograph. We obtain long-slit spectra at the base of five T Tauri jets to determine if there is a difference in radial velocity between the jet borders which may be interpreted as a rotation signature. These observations are extremely challenging and push the limits of current instrumentation, but have the potential to provide long-awaited observational support for the magnetocentrifugal mechanism of jet launching in which jets remove angular momentum from protostellar systems. We successfully detect all five jet targets (from RW Aur, HN Tau, DP Tau, and CW Tau) in several near-ultraviolet emission lines, including the strong Mg II doublet. However, only RW Aur's bipolar jet presents a sufficiently high signal-to-noise ratio to allow for analysis. The approaching jet lobe shows a difference of 10kms-1 in a direction which agrees with the disk rotation sense, but is opposite to previously published optical measurements for the receding jet. The near-ultraviolet difference is not found six months later, nor is it found in the fainter receding jet. Overall, in the case of RW Aur, differences are not consistent with a simple jet rotation interpretation. Indeed, given the renowned complexity and variability of this system, it now seems likely that any rotation signature is confused by other influences, with the inevitable conclusion that RW Aur is not suited to a jet rotation study. © 2012. The American Astronomical Society. All rights reserved.


Imanishi M.,Japan National Astronomical Observatory | Imanishi M.,Graduate University for Advanced Studies | Maiolino R.,National institute for astrophysics | Nakagawa T.,Japan Aerospace Exploration Agency
Astrophysical Journal | Year: 2010

We present the results of Spitzer Infrared Spectrograph low-resolution infrared 5-35 μm spectroscopy of 17 nearby ultraluminous infrared galaxies (ULIRGs) at z < 0.2, optically classified as non-Seyferts. The presence of optically elusive, but intrinsically luminous, buried active galactic nuclei (AGNs) is investigated, based on the strengths of polycyclic aromatic hydrocarbon emission and silicate dust absorption features detected in the spectra. The signatures of luminous buried AGNs, whose intrinsic luminosities range up to 1012 L ⊙, are found in eight sources. We combine these results with those of our previous research to investigate the energy function of buried AGNs in a complete sample of optically non-Seyfert ULIRGs in the local universe at z < 0.3 (85 sources). We confirm a trend that we previously discovered: that buried AGNs are more common in galaxies with higher infrared luminosities. Because optical Seyferts also show a similar trend, we argue more generally that the energetic importance of AGNs is intrinsically higher in more luminous galaxies, suggesting that the AGN-starburst connections are luminosity dependent. This may be related to the stronger AGN feedback scenario in currently more massive galaxy systems, as a possible origin of the galaxy downsizing phenomenon. © 2010 The American Astronomical Society.


Milani A.,University of Pisa | Knezevic Z.,Astronomical Observatory | Novakovic B.,Astronomical Observatory | Cellino A.,National institute for astrophysics
Icarus | Year: 2010

To try to understand the dynamical and collisional evolution of the Hungaria asteroids we have built a large catalog of accurate synthetic proper elements. Using the distribution of the Hungaria, in the spaces of proper elements and of proper frequencies, we can study the dynamical boundaries and the internal structure of the Hungaria region, both within a purely gravitational model and also showing the signature of the non-gravitational effects. We find a complex interaction between secular resonances, mean motion resonances, chaotic behavior and Yarkovsky-driven drift in semimajor axis. We also find a rare occurrence of large scale instabilities, leading to escape from the region. This allows to explain the complex shape of a grouping which we suggest is a collisional family, including most Hungaria but by no means all; we provide an explicit list of non-members of the family. There are finer structures, of which the most significant is a set of very close asteroid couples, with extremely similar proper elements. Some of these could have had, in a comparatively recent past, very close approaches with low relative velocity. We argue that the Hungaria, because of the favorable observing conditions, may soon become the best known sub-group of the asteroid population. © 2010 Elsevier Inc.


He J.-H.,National institute for astrophysics | He J.-H.,Durham University | Li B.,Durham University | Hawken A.J.,National institute for astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Using N-body simulations, we measure the power spectrum of the effective dark matter density field, which is defined through the modified Poisson equation in f(R) cosmologies. We find that, when compared to the conventional dark matter power spectrum, the effective power spectrum deviates more significantly from the ΛCDM model. For models with fR0=-10-4, the deviation can exceed 150%, while the deviation of the conventional matter power spectrum is less than 50%. Even for models with fR0=-10-6, for which the conventional matter power spectrum is very close to the ΛCDM prediction, the effective power spectrum shows sizeable deviations. Our results indicate that traditional analyses based on the dark matter density field may seriously underestimate the impact of f(R) gravity on galaxy clustering. We therefore suggest the use of the effective density field in such studies. In addition, based on our findings, we also discuss several possible methods of making use of the differences between the conventional and effective dark matter power spectra in f(R) gravity to discriminate the theory from the ΛCDM model. © 2015 American Physical Society.


He J.-H.,National institute for astrophysics | Hawken A.J.,National institute for astrophysics | Li B.,Durham University | Guzzo L.,National institute for astrophysics
Physical Review Letters | Year: 2015

We introduce the idea of an effective dark matter halo catalog in f(R) gravity, which is built using the effective density field. Using a suite of high resolution N-body simulations, we find that the dynamical properties of halos, such as the distribution of density, velocity dispersion, specific angular momentum and spin, in the effective catalog of f(R) gravity closely mimic those in the cold dark matter model with a cosmological constant (ΛCDM). Thus, when using effective halos, an f(R) model can be viewed as a ΛCDM model. This effective catalog therefore provides a convenient way for studying the baryonic physics, the galaxy halo occupation distribution and even semianalytical galaxy formation in f(R) cosmologies. © 2015 American Physical Society. © 2015 American Physical Society.


Kofidis E.,University of Piraeus | Katselis D.,KTH Royal Institute of Technology | Rontogiannis A.,National institute for astrophysics | Theodoridis S.,National and Kapodistrian University of Athens
Signal Processing | Year: 2013

Filter bank-based multicarrier communications (FBMC) have recently attracted increased interest in both wired (e.g., xDSL, PLC) and wireless (e.g., cognitive radio) applications, due to their enhanced flexibility, higher spectral efficiency, and better spectral containment compared to conventional OFDM. A particular type of FBMC, the so-called FBMC/OQAM or OFDM/OQAM system, consisting of pulse shaped OFDM carrying offset QAM (OQAM) symbols, has received increasing attention due to, among other features, its higher spectral efficiency and implementation simplicity. It suffers, however, from an imaginary inter-carrier/inter-symbol interference that complicates signal processing tasks such as channel estimation. This paper focuses on channel estimation for OFDM/OQAM systems based on a known preamble. A review of the existing preamble structures and associated channel estimation methods is given, for both single- (SISO) and multiple-antenna (MIMO) systems. The various preambles are compared via simulations in both mildly and highly frequency selective channels. © 2013 Elsevier B.V.


Vignali C.,University of Bologna | Vignali C.,National institute for astrophysics | Alexander D.M.,Durham University | Gilli R.,National institute for astrophysics | Pozzi F.,University of Bologna
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present new and archival Chandra snapshot (≈10 ks each) observations of 15 optically identified [from the Sloan Digital Sky Survey (SDSS)] Type 2 quasars at z = 0.40-0.73. When combined with existing X-ray data, this work provides complete X-ray coverage for all 25 radio-quiet Type 2 quasars with logL[O III] > 9.28 L⊙ from Zakamska et al. Two targets out of 15 were not detected by Chandra and most of the remaining sources are X-ray weak, with nine having less than 10 counts in the 0.5-8 keV band. Low-to moderate-quality spectral analysis was limited to three sources, whose properties are consistent with the presence of column densities in the range NH ≈ 1022-1023 cm-2 in the source rest frame. If the [OIII] luminosity is a reliable proxy for the intrinsic X-ray luminosity, the current X-ray data indicate that Compton-thick quasars may hide among ≈65 per cent of the SDSS Type 2 quasar population (LX,meas/LX,[OIII] < 0.01); however, since the Type 2 quasar sample is selected on [O III] luminosity, the estimated Compton-thick quasar fraction may be overestimated. Using archival Spitzer observations, we find that ≈50 per cent of SDSS Type 2 quasars appear to be obscured by Compton-thick material based on both the LX,meas/LX,mid-IR (where mid-IR corresponds to rest frame 12.3 μm) and LX,meas/LX,[OIII] ratios. We use this information to provide an estimate of the Compton-thick quasar number density at z ≈ 0.3-0.8, which we find is in broad agreement with the expectations from X-ray background models. © 2010 The Authors. Journal compilation. © 2010 RAS.


Ferrario L.,Australian National University | de Martino D.,National institute for astrophysics | Gansicke B.T.,University of Warwick
Space Science Reviews | Year: 2015

In this paper we review the current status of research on the observational and theoretical characteristics of isolated and binary magnetic white dwarfs (MWDs). Magnetic fields of isolated MWDs are observed to lie in the range 103–109 G. While the upper limit cutoff near 109 G appears to be real, the lower limit is more difficult to investigate. The incidence of magnetism below a few 103 G still needs to be established by sensitive spectropolarimetric surveys-conducted on 8 m class telescopes. Highly magnetic WDs tend to exhibit a complex and non-dipolar field structure with some objects showing the presence of higher order multipoles. There is no evidence that fields of highly magnetic WDs decay over time, which is consistent with the estimated Ohmic decay times scales of ∼1011 yrs. The slow rotation periods (∼100 yrs) inferred for a large number of isolated MWDs in comparison to those of non-magnetic WDs (a few days) suggest that strong magnetic fields augment the braking of the stellar core. MWDs, as a class, also appear to be more massive (0.784±0.047 M⊙) than their weakly or non-magnetic counterparts (0.663±0.136 M⊙). MWDs are also found in binary systems where they accrete matter from a low-mass donor star. These binaries, called magnetic Cataclysmic Variables (MCVs), comprise about 20–25 % of all known CVs. Zeeman and cyclotron spectroscopy of MCVs have revealed the presence of fields in the range ∼7–230 MG. Complex field geometries have been inferred in the high field MCVs (the polars) whilst magnetic field strength and structure in the lower field group (intermediate polars, IPs) are much harder to establish. The MCVs exhibit an orbital period distribution which is similar to that of non magnetic CVs. Polars dominate the distribution at orbital periods ≲4 h and IPs at longer periods. It has been argued that IPs above the 2–3 hr CV period gap with magnetic moments ≳ 5×1033 G cm3 may eventually evolve into polars. It is vital to enlarge the still incomplete sample of MCVs to understand not only their accretion processes but also their evolution. The origin of fields in MWDs is still being debated. While the fossil field hypothesis remains an attractive possibility, field generation within the common envelope of a binary system has been gaining momentum, since it would explain the absence of MWDs paired with non-degenerate companions and also the lack of relatively wide pre-MCVs. © 2015, Springer Science+Business Media Dordrecht.


Burlon D.,Max Planck Institute for Extraterrestrial Physics | Ajello M.,Kavli Institute for Particle Astrophysics and Cosmology | Greiner J.,Max Planck Institute for Extraterrestrial Physics | Comastri A.,National institute for astrophysics | And 3 more authors.
Astrophysical Journal | Year: 2011

It is well accepted that unabsorbed as well as absorbed active galactic nuclei (AGNs) are needed to explain the nature and shape of the Cosmic X-ray background (CXB), even if the fraction of highly absorbed objects (dubbed Compton-thick sources) still substantially escapes detection. We derive and analyze the absorption distribution using a complete sample of AGNs detected by Swift-BAT in the first three years of the survey. The fraction of Compton-thick AGNs represents only 4.6% of the total AGN population detected by Swift-BAT. However, we show that once corrected for the bias against the detection of very absorbed sources the real intrinsic fraction of Compton-thick AGNs is 20 +9-6%. We proved for the first time (also in the Burst Alert Telescope (BAT) band) that the anti-correlation of the fraction of absorbed AGNs and luminosity is tightly connected to the different behavior of the X-ray luminosity functions (XLFs) of absorbed and unabsorbed AGNs. This points toward a difference between the two subsamples of objects with absorbed AGNs being, on average, intrinsically less luminous than unobscured ones. Moreover, the XLFs show that the fraction of obscured AGNs might also decrease at very low luminosity. This can be successfully interpreted in the framework of a disk cloud outflow scenario as the disappearance of the obscuring region below a critical luminosity. Our results are discussed in the framework of population synthesis models and the origin of the CXB. © 2011. The American Astronomical Society. All rights reserved. Printedin the U.S.A.


Stanghellini L.,National Optical Astronomy Observatory | Magrini L.,National institute for astrophysics | Casasola V.,National institute for astrophysics | Villaver E.,Autonomous University of Madrid
Astronomy and Astrophysics | Year: 2014

Aims. We present a new set of weak-line abundances of HII regions in M 81, which are based on Gemini Multi-Object Spectrograph (GMOS) observations. The aim is to derive plasma and abundance analysis for a sizable set of emission-line targets to study the galactic chemical contents in the framework of galactic metallicity gradients. Methods. We used the weak-line abundance approach by deriving electron density and temperatures for several HII regions in M 81. Our gradient analysis is based on oxygen abundances. Results. Together with a set of HII region abundances determined similarly by us with Multi-Mirror Telescope (MMT) spectra, the new data yield a radial oxygen gradient of -0.088 ± 0.013 dex kpc-1, which is steeper than the metallicity gradient obtained for planetary nebulae (-0.044 ± 0.007 dex? kpc-1). This result could be interpreted as gradient evolution with time: Models of galactic evolution with inside-out disk formation associated to pre-enriched gas infall would produce such a difference in gradients, although stellar migration effects would also induce a difference in the metallicity gradients between the old and young populations. Conclusions. By comparing the M 81 metallicity gradients with those of other spiral galaxies, which were all consistently derived from weak-line analysis, we can infer that a similar gradient difference is common among spirals. The metallicity gradient slopes for HII regions and PNe seem to be steeper in M 81 than in other galactic disks, which is probably because M 81 belongs to a galaxy group. We also found that M 81 has experienced an average oxygen enrichment of 0.14 ± 0.08 dex in the spatial domain defined by the observations. Our data are compatible with a break in the radial oxygen gradient slope around R25 as inferred by other authors both in M 81 and in other galaxies. © 2014 ESO.


Ivison R.J.,Astronomy Technology Center | Ivison R.J.,University of Edinburgh | Papadopoulos P.P.,Argelander Institute For Astronomie | Smail I.,Durham University | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We report the results of a pilot study with the Expanded Very Large Array (EVLA) of 12CO J= 1-0 emission from four submillimetre-selected galaxies at z= 2.2-2.5, each with an existing detection of 12CO J= 3-2, one of which comprises two distinct spatial components. Using the EVLA's most compact configuration, we detect strong, broad [medians: 990kms-1 full width at zero intensity; 540kms-1 full width at half-maximum (FWHM)]J= 1-0 line emission from all of our targets - coincident in position and velocity with their J= 3-2 emission. The median linewidth ratio, σ1-0/σ3-2= 1.15 ± 0.06, suggests that the J= 1-0 is more spatially extended than the J= 3-2 emission, a situation confirmed by our maps which reveal velocity structure in several cases and typical sizes of ∼16kpc FWHM. The median brightness temperature (Tb) ratio is r3-2/1-0= 0.55 ± 0.05, consistent with local galaxies with LIR > 1011L⊙, noting that our value may be biased high because of the J= 3-2 based sample selection. Naively, this suggests gas masses roughly two times higher than estimates made using higher J transitions of CO, with the discrepancy due entirely to the difference in assumed Tb ratio. We also estimate molecular gas masses using the 12CO J= 1-0 line and the observed global Tb ratios, assuming standard underlying Tb ratios for the non-star-forming and star-forming gas phases as well as a limiting star formation efficiency for the latter in all systems, i.e. without calling upon XCO (≡α). Using this new method, we find a median molecular gas mass of (2.5 ± 0.8) × 1010M⊙, with a plausible range stretching up to three times higher. Even larger masses cannot be ruled out, but are not favoured by dynamical constraints: the median dynamical mass within R∼ 7kpc for our sample is (2.3 ± 1.4) × 1011M⊙ or ∼6 times more massive than UV-selected galaxies at this epoch. We examine the Schmidt-Kennicutt (S-K) relation for all the distant galaxy populations for which CO J= 1-0 or J= 2-1 data are available, finding small systematic differences between galaxy populations. These have previously been interpreted as evidence for different modes of star formation, but we argue that these differences are to be expected, given the still considerable uncertainties, certainly when considering the probable excitation biases due to the molecular lines used, and the possibility of sustained S-K offsets during the evolution of individual gas-rich systems. Finally, we discuss the morass of degeneracies surrounding molecular gas mass estimates, the possibilities for breaking them, and the future prospects for imaging and studying cold, quiescent molecular gas at high redshifts. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


He J.-H.,National institute for astrophysics | Li B.,Durham University | Hawken A.J.,National institute for astrophysics | Granett B.R.,National institute for astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

We reexamine the screening mechanism in f(R) gravity using N-body simulations. By explicitly examining the relation between the extrascalar field δfR and the gravitational potential φ in the perturbed Universe, we find that the relation between these two fields plays an important role in understanding the screening mechanism. We show that the screening mechanism in f(R) gravity depends mainly on the depth of the potential well and find a useful condition for identifying unscreened haloes in simulations. We also discuss the potential application of our results to real galaxy surveys. © 2014 American Physical Society.


Milani A.,University of Pisa | Cellino A.,National institute for astrophysics | Knezevic Z.,Astronomical Observatory | Novakovic B.,University of Belgrade | And 2 more authors.
Icarus | Year: 2014

The number of asteroids with accurately determined orbits increases fast, and this increase is also accelerating. The catalogs of asteroid physical observations have also increased, although the number of objects is still smaller than in the orbital catalogs. Thus it becomes more and more challenging to perform, maintain and update a classification of asteroids into families. To cope with these challenges we developed a new approach to the asteroid family classification by combining the Hierarchical Clustering Method (HCM) with a method to add new members to existing families. This procedure makes use of the much larger amount of information contained in the proper elements catalogs, with respect to classifications using also physical observations for a smaller number of asteroids.Our work is based on a large catalog of high accuracy synthetic proper elements (available from AstDyS), containing data for >330,000 numbered asteroids. By selecting from the catalog a much smaller number of large asteroids, we first identify a number of core families; to these we attribute the next layer of smaller objects. Then, we remove all the family members from the catalog, and reapply the HCM to the rest. This gives both satellite families which extend the core families and new independent families, consisting mainly of small asteroids. These two cases are discriminated by another step of attribution of new members and by merging intersecting families. This leads to a classification with 128 families and currently 87,095 members. The number of members can be increased automatically with each update of the proper elements catalog; changes in the list of families are not automated.By using information from absolute magnitudes, we take advantage of the larger size range in some families to analyze their shape in the proper semimajor axis vs. inverse diameter plane. This leads to a new method to estimate the family age, or ages in cases where we identify internal structures. The analysis of the plot above evidences some open problems but also the possibility of obtaining further information of the geometrical properties of the impact process. The results from the previous steps are then analyzed, using also auxiliary information on physical properties including WISE albedos and SDSS color indexes. This allows to solve some difficult cases of families overlapping in the proper elements space but generated by different collisional events.The families formed by one or more cratering events are found to be more numerous than previously believed because the fragments are smaller. We analyze some examples of cratering families (Massalia, Vesta, Eunomia) which show internal structures, interpreted as multiple collisions. We also discuss why Ceres has no family. © 2014 Elsevier Inc.


Novakovic B.,University of Belgrade | Cellino A.,National institute for astrophysics | Knezevic Z.,Astronomical Observatory
Icarus | Year: 2011

We present a new classification of families identified among the population of high-inclination asteroids. We computed synthetic proper elements for a sample of 18,560 numbered and multi-opposition objects having sine of proper inclination greater than 0.295. We considered three zones at different heliocentric distances (inner, intermediate and outer region) and used the standard approach based on the Hierarchical Clustering Method (HCM) to identify families in each zone. In doing so, we used slightly different approach with respect to previously published methodologies, to achieve a more reliable and robust classification. We also used available SDSS color data to improve membership and identify likely family interlopers. We found a total of 38 families, as well as a significant number of clumps and clusters deserving further investigation. © 2011 Elsevier Inc.


Massaro F.,Kavli Institute for Particle Astrophysics and Cosmology | D'Abrusco R.,Smithsonian Astrophysical Observatory | Giroletti M.,National institute for astrophysics | Paggi A.,Smithsonian Astrophysical Observatory | And 5 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

About one-third of the γ-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) have no firmly established counterpart at lower energies and so are classified as unidentified gamma-ray sources (UGSs). Here, we propose a new approach to find candidate counterparts for the UGSs based on the 325 MHz radio survey performed with the Westerbork Synthesis Radio Telescope in the northern hemisphere. First, we investigate the low-frequency radio properties of blazars, the largest known population of γ-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO Very Large Array Sky Survey. We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in the literature to look for infrared and optical counterparts of the γ-ray blazar candidates selected using the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research, we identify 23 new γ-ray blazar candidates out of the 32 UGSs investigated. Comparison with previous results on the UGSs is also presented. Finally, we speculate on the advantages of using low-frequency radio observations to associate UGSs and to search for γ-ray pulsar candidates. © 2013. The American Astronomical Society. All rights reserved.


D'Abrusco R.,Smithsonian Astrophysical Observatory | Massaro F.,Kavli Institute for Particle Astrophysics and Cosmology | Paggi A.,Smithsonian Astrophysical Observatory | Masetti N.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 4 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

We present a new method for identifying blazar candidates by examining the locus, i.e., the region occupied by the Fermi γ-ray blazars in the three-dimensional color space defined by the WISE infrared colors. This method is a refinement of our previous approach that made use of the two-dimensional projection of the distribution of WISE γ-ray-emitting blazars (the Strip) in the three WISE color-color planes. In this paper, we define the three-dimensional locus by means of a principal component analysis of the color distribution of a large sample of blazars composed of all the ROMA-BZCAT sources with counterparts in the WISE All-Sky Catalog associated with γ-ray sources in the second Fermi-LAT catalog (2FGL; the WISE Fermi blazars sample, WFB). Our new procedure yields a total completeness of c tot ∼ 81% and a total efficiency of e tot ∼ 97%. We also obtain local estimates of the efficiency and completeness as functions of the WISE colors and galactic coordinates of the candidate blazars. The catalog of all WISE candidate blazars associated with the WFB sample is also presented, complemented by archival multi-frequency information for the alternative associations. Finally, we apply the new association procedure to all γ-ray blazars in the 2FGL and provide a catalog containing all the γ-ray candidate blazars selected according to our procedure. © 2013. The American Astronomical Society. All rights reserved.


Paggi A.,Smithsonian Astrophysical Observatory | Massaro F.,Kavli Institute for Particle Astrophysics and Cosmology | D'Abrusco R.,Smithsonian Astrophysical Observatory | Smith H.A.,Smithsonian Astrophysical Observatory | And 4 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

A significant fraction (∼30%) of the high-energy γ-ray sources listed in the second Fermi Large Area Telescope (LAT) catalog are still of unknown origin, having not yet been associated with counterparts at lower energies. To investigate the nature of these enigmatic sources, we present an extensive search of X-ray sources lying in the positional uncertainty region of a selected sample of these unidentified gamma-ray sources (UGSs) that makes use of all available observations performed by the Swift X-ray Telescope before 2013 March 31, available for 205 UGSs. To detect the fainter sources, we merged all the observations covering the Fermi LAT positional uncertainty region at a 95% level of confidence of each UGS. This yields a catalog of 357 X-ray sources, finding candidate X-ray counterparts for ∼70% of the selected sample. In particular, 25% of the UGSs feature a single X-ray source within their positional uncertainty region, while 45% have multiple X-ray sources. For each X-ray source, we also looked in the corresponding Swift UVOT merged images for optical and ultraviolet counterparts, also performing source photometry. We found ultraviolet-optical correspondences for ∼70% of the X-ray sources. We searched several major radio, infrared, optical, and ultraviolet surveys for possible counterparts within the positional error of the sources in the X-ray catalog to obtain additional information on their nature. Applying the kernel density estimation technique to infrared colors of Wide-Field Infrared Survey Explorer counterparts of our X-ray sources we select six γ-ray blazar candidates. In addition, comparing our results with previous analyses, we select 11 additional γ-ray blazar candidates. © 2013. The American Astronomical Society. All rights reserved.


Ferreras I.,University College London | La Barbera F.,National institute for astrophysics | de la Rosa I.G.,Institute of Astrophysics of Canarias | de la Rosa I.G.,University of La Laguna | And 6 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

An essential component of galaxy formation theory is the stellarinitial mass function (IMF) that describes the parent distribution ofstellar mass in star-forming regions. We present observational evidence in a sample of early-type galaxies (ETGs) of a tight correlation between central velocity dispersion and the strength of several absorption features sensitive to the presence of low-mass stars. Our samplecomprises ~40 000 ETGs from the Spheroids Panchromatic Investigation in Different Environmental Regions survey (z ∼ 0.1). The data-extracted from the Sloan Digital Sky Survey-are combined, rejecting both noisy data, and spectra with contamination from telluric lines, resulting in a set of 18 stacked spectra at high signal-to-noise ratio (S/N ≳ 400å-1). A combined analysis of IMF-sensitive line strengths and spectral fitting is performed with the latest state-of-the-art population synthesis models (an extended version of the MILES models). Asignificant trend is found between IMF slope and velocity dispersion, towards an excess of low-mass stars in the most massive galaxies. Although we emphasize that accurate values of the IMF slope will requirea detailed analysis of chemical composition (such as [α/Fe] or even individual element abundance ratios), the observed trends suggest thatlow-mass ETGs are better fitted by a Kroupa-like IMF, whereas massivegalaxies require bottom-heavy IMFs, exceeding the Salpeter slope at σ ≳ 200 km s-1. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Massaro F.,Kavli Institute for Particle Astrophysics and Cosmology | Giroletti M.,National institute for astrophysics | Paggi A.,Smithsonian Astrophysical Observatory | D'Abrusco R.,Smithsonian Astrophysical Observatory | And 2 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

Blazars are the most extreme class of active galactic nuclei. Despite a previous investigation at 102 MHz for a small sample of BL Lac objects and our recent analysis of blazars detected in the Westerbork Northern Sky Survey, a systematic study of the blazar spectral properties at frequencies below 100 MHz has been never carried out. In this paper, we present the first analysis of the radio spectral behavior of blazars based on the recent Very Large Array Low-frequency Sky Survey (VLSS) at 74 MHz. We search for blazar counterparts in the VLSS catalog, confirming that they are detected at 74 MHz. We then show that blazars present radio-flat spectra (i.e., radio spectral indices of 0.5) when evaluated, which also about an order of magnitude in frequency lower than previous analyses. Finally, we discuss the implications of our findings in the context of the blazars-radio galaxies connection since the low-frequency radio data provide a new diagnostic tool to verify the expectations of the unification scenario for radio-loud active galaxies. © 2013. The American Astronomical Society. All rights reserved..


Massaro F.,Kavli Institute for Particle Astrophysics and Cosmology | D'Abrusco R.,Smithsonian Astrophysical Observatory | Paggi A.,Smithsonian Astrophysical Observatory | Masetti N.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 5 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

A significant fraction (∼30%) of the high-energy gamma-ray sources listed in the second Fermi Large Area Telescope catalog (2FGL) are still of unknown origin, being not yet associated with counterparts at low energies. We recently developed a new association method to identify if there is a γ-ray blazar candidate within the positional uncertainty region of a generic 2FGL source. This method is entirely based on the discovery that blazars have distinct infrared colors with respect to other extragalactic sources found, thanks to the Wide-field Infrared Survey Explorer (WISE) all-sky observations. Several improvements have also been performed to increase the efficiency of our method in recognizing γ-ray blazar candidates. In this paper we applied our method to two different samples, the first constituted by unidentified γ-ray sources (UGSs), and the second by active galaxies of uncertain type, both listed in the 2FGL. We present a catalog of IR counterparts for ∼20% of the UGSs investigated. Then, we also compare our results for the associated sources with those present in the literature. In addition, we illustrate the extensive archival research carried out to identify the radio, infrared, optical, and X-ray counterparts of the WISE-selected, γ-ray blazar candidates. Finally, we discuss the future developments of our method based on ground-based follow-up observations. © 2013. The American Astronomical Society. All rights reserved.


Biffi V.,International School for Advanced Studies | Biffi V.,Autonomous University of Madrid | Maio U.,National institute for astrophysics | Maio U.,Leibniz Institute for Astrophysics Potsdam
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study the baryonic, chemical and dynamical properties of a significantly large sample of early protogalaxies in the first 500 Myr of the Universe (redshift z ≳ 9), obtained from highresolution numerical, N-body, hydrodynamical, chemistry simulations including atomic and molecular networks, gas cooling, star formation, stellar evolution and metal spreading for Population III and Population II-I regimes according to proper stellar yields and lifetimes.We find that first star formation events take place in haloes with dark matter massMDM > 2 × 106Mo. Early star-forming objects have: molecular fractions from xmol ≲ 10-4 in quiescent structures up to xmol ≳0.1 in active regions; star formation rates (SFR)∼10-8-10--3M-4 yr-1; and metallicities in the range ∼10-8-10--2ZO. Roughly ∼10 per cent of high-z haloes host Population II-I star formation and dominate the cosmic SFR density. They usually are bursty objects with mean specific SFR around ∼10 Gyr-1 at z ∼ 9 and increasing with redshift up to ∼102 Gyr-1. Stellar feedback effects alter the baryonic content of the haloes and locally affect their chemical and thermodynamical properties, as reflected by the broadening of various physical relations. The establishment of gaseous rotationally supported cores is quite uncommon, weakly related to the large-scale dark matter behaviour and evolving in an intermittent fashion. The colder, molecular-rich phase tends to maintain any established rotational motion longer with respect to the hotter, metal-rich component, which is very sensitive to environmental processes. While the fraction of haloes featuring a significant amount of corotating, molecular-rich gas increases with cosmic time (from a fewper cent at z ∼ 20 up to ∼5-15 per cent at z ∼ 9), the chaotic nature of metal-enriched material does not lead to particular trends. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Feruglio C.,University Paris Diderot | Daddi E.,University Paris Diderot | Fiore F.,National institute for astrophysics | Alexander D.M.,Durham University | And 2 more authors.
Astrophysical Journal Letters | Year: 2011

We report the detection of the 6.4 keV iron Kα emission line in two infrared-luminous, massive, star-forming BzKgalaxies at z = 2.578 and z = 2.90 in the CDF-S. The Chandra 4 Ms spectra of BzK4892 and BzK8608 show a reflection-dominated continuum with strong iron lines, with rest-frame equivalent widths EW 2.3 keV and 1.2 keV, respectively, demonstrating Compton thick (CT) obscuration of the central active galactic nucleus (AGN). For BzK8608, the line identification closely matches the existing photometric redshift derived from the stellar emission. We use the observed luminosities of the iron Kα line, of the rest-frame mid-IR continuum and of the UV rest-frame narrow emission lines to infer intrinsic L 2-10 keV ≳ 1044 erg s-1, about 1.0-2.5 dex larger than the observed ones, hence confirming the presence of an absorber with N H> 1024 cm-2. The two BzKgalaxies have stellar masses of 5 × 1010 M and, based on Very Large Array 1.4 GHz and submillimeter 870 μm observations, they appear to host vigorous starburst activity with star formation rate 300-700 M r-1 that is also optically thick. We estimate that the AGN might also conceivably account for an important fraction of the bolometric far-IR emission of the galaxies. The implied volume density of CT AGN with L 2-10 keV>1044 erg s-1 is in agreement with predictions from X-ray background synthesis models. These sources provide one of the first clear-cut observations of the long-sought phase of simultaneous, heavily obscured quasar and star formation activity, predicted by models of massive galaxy evolution at high redshifts. © 2011. The American Astronomical Society. All rights reserved.


Weinmann S.M.,Max Planck Institute for Astrophysics | Kauffmann G.,Max Planck Institute for Astrophysics | von der Linden A.,Kavli Institute for Particle Astrophysics and Cosmology | De Lucia G.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We investigate how the specific star formation rates of galaxies of different masses depend on cluster-centric radius and on the central/satellite dichotomy in both field and cluster environments. Recent data from a variety of sources, including the cluster catalogue of von der Linden et al., are compared to the semi-analytic models of De Lucia & Blaizot. We find that these models predict too many passive satellite galaxies in clusters, too few passive central galaxies with low stellar masses and too many passive central galaxies with high masses. We then outline a series of modifications to the model necessary to solve these problems: (a) instead of instantaneous stripping of the external gas reservoir after a galaxy becomes a satellite, the gas supply is assumed to decrease at the same rate that the surrounding halo loses mass due to tidal stripping and (b) the active galactic nuclei (AGN) feedback efficiency is lowered to bring the fraction of massive passive centrals in better agreement with the data. We also allow for radio mode AGN feedback in satellite galaxies. (c) We assume that satellite galaxies residing in host haloes with masses below 1012 h-1 M⊙ do not undergo any stripping. We highlight the fact that in low-mass galaxies, the external reservoir is composed primarily of gas that has been expelled from the galactic disc by supernovae-driven winds. This gas must remain available as a future reservoir for star formation, even in satellite galaxies. Finally, we present a simple recipe for the stripping of gas and dark matter in satellites that can be used in models where subhalo evolution is not followed in detail. © 2010 The Authors. Journal compilation © 2010 RAS.


Massaro F.,Kavli Institute for Particle Astrophysics and Cosmology | D'Abrusco R.,Smithsonian Astrophysical Observatory | Paggi A.,Smithsonian Astrophysical Observatory | Masetti N.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 4 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

Nearly one-third of the γ-ray sources detected by Fermi are still unidentified, despite significant recent progress in this area. However, all of the γ-ray extragalactic sources associated in the second Fermi-LAT catalog have a radio counterpart. Motivated by this observational evidence, we investigate all the radio sources of the major radio surveys that lie within the positional uncertainty region of the unidentified γ-ray sources (UGSs) at a 95% level of confidence. First, we search for their infrared counterparts in the all-sky survey performed by the Wide-field Infrared Survey Explorer (WISE) and then we analyze their IR colors in comparison with those of the known γ-ray blazars. We propose a new approach, on the basis of a two-dimensional kernel density estimation technique in the single [3.4]-[4.6]-[12] μm WISE color-color plot, replacing the constraint imposed in our previous investigations on the detection at 22 μm of each potential IR counterpart of the UGSs with associated radio emission. The main goal of this analysis is to find distant γ-ray blazar candidates that, being too faint at 22 μm, are not detected by WISE and thus are not selected by our purely IR-based methods. We find 55 UGSs that likely correspond to radio sources with blazar-like IR signatures. An additional 11 UGSs that have blazar-like IR colors have been found within the sample of sources found with deep recent Australia Telescope Compact Array observations. © 2013. The American Astronomical Society. All rights reserved.


Weidner C.,Institute of Astrophysics of Canarias | Weidner C.,University of La Laguna | Ferreras I.,University College London | Vazdekis A.,Institute of Astrophysics of Canarias | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Recent evidence based independently on spectral line strengths and dynamical modelling point towards a non-universal stellar initial mass function (IMF), probably implying an excess of low-mass stars in elliptical galaxies with a high velocity dispersion. Here, we show that a time-independent bottom-heavy IMF is compatible neither with the observed metal-rich populations found in giant ellipticals nor with the number of stellar remnants observed within these systems. We suggest a two-stage formation scenario involving a time-dependent IMF to reconcile these observational constraints. In this model, an early strong starbursting stage with a top-heavy IMF is followed by a more prolonged stage with a bottom-heavy IMF. Such model is physically motivated by the fact that a sustained high star formation will bring the interstellar medium to a state of pressure, temperature and turbulence that can drastically alter the fragmentation of the gaseous component into small clumps, promoting the formation of low-mass stars. This toymodel is in good agreement with the different observational constrains on massive elliptical galaxies, such as age, metallicity, α-enhancement, mass-to-light ratio or the mass fraction of the stellar component in low-mass stars. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Valle M.D.,National institute for astrophysics | Valle M.D.,International Center for Relativistic Astrophysics
International Journal of Modern Physics D | Year: 2011

In this paper I shall shortly review the observational status of the Supernova and Gamma-ray Bursts connection including the most recent observations: the discovery of a new case of association at z = 0.53 (SN 2008 hw/GRB 081007) and the case of SN 2008D associated with the XRF 080109, a borderline object which may link GRBs with "standard" core-collapse events. © 2011 World Scientific Publishing Company.


Smart R.L.,National institute for astrophysics | Nicastro L.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomy and Astrophysics | Year: 2014

Aims. We describe the production of the Initial Gaia Source List (IGSL) used both as the starting point for observation-matching in the Gaia data processing and as a comparison catalog to trigger early science alerts. Methods. The IGSL was compiled from large scale public catalogs and a few specific catalogs provided by the Gaia Consortium. For all entries, a Gaia G magnitude is estimated and all objects with a G< 21.0 were included. Results. The catalog has 1222598530 entries with the J2000 ICRF positions, proper motions, classification (star/non-star), and estimates of the Gaia G, Gaia Grvs, Guide Star Catalog red (RF) and blue (BJ) magnitudes. It is available from the Centre de Données astronomiques de Strasbourg. © 2014 ESO.


Greco A.,University of Calabria | Matthaeus W.H.,University of Delaware | D'Amicis R.,National institute for astrophysics | Servidio S.,University of Calabria | Dmitruk P.,FCEyN
Astrophysical Journal | Year: 2012

The formation of coherent structures in turbulence is a signature of a developing cascade and therefore might be observable by analyzing inner heliospheric solar wind turbulence. To test this idea, data from the Helios 2 mission, for six streams of solar wind at different heliocentric distances and of different velocities, were subjected to statistical analysis using the partial variance of increments (PVI) approach. We see a clear increase of the PVI distribution function versus solar wind age for higher PVI cutoff, indicating development of non-Gaussian coherent structures. The plausibility of this interpretation is confirmed by a similar behavior observed in two-dimensional magnetohydrodynamics simulation data at corresponding dimensionless nonlinear times. © 2012. The American Astronomical Society. All rights reserved.


Malizia A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Molina M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Bassani L.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Stephen J.B.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 3 more authors.
Astrophysical Journal Letters | Year: 2014

In this Letter we present the primary continuum parameters, the photon index Γ, and the high-energy cut-off E c of 41 type-1 Seyfert galaxies extracted from the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) complete sample of active galactic nuclei (AGNs). We performed broadband (0.3-100 keV) spectral analysis by simultaneously fitting the soft and hard X-ray spectra obtained by XMM and INTEGRAL/IBIS-Swift/BAT, respectively, in order to investigate the general properties of these parameters, in particular their distribution and mean values. We find a mean photon index of 1.73 with a standard deviation of 0.17 and a mean high-energy cut-off of 128 keV with a standard deviation of 46 keV for the whole sample. This is the first time that the cut-off energy is constrained in such a large number of AGNs. We have 26 measurements of the cut-off, which corresponds to 63% of the entire sample, distributed between 50 and 200 keV. There are a further 11 lower limits mostly below 300 keV. Using the main parameters of the primary continuum, we have been able to obtain the actual physical parameters of the Comptonizing region, i.e., the plasma temperature kTe from 20 to 100 keV and the optical depth τ < 4. Finally, with the high signal-to-noise ratio spectra starting to come from NuSTAR it will soon be possible to better constrain the cut-off values in many AGNs, allowing the determination of more physical models and thus better understand the continuum emission and geometry of the region surrounding black holes. © 2014. The American Astronomical Society. All rights reserved..


Cellino A.,National institute for astrophysics | Bagnulo S.,Armagh Observatory | Tanga P.,University of Nice Sophia Antipolis | Novakovic B.,University of Belgrade | Delbo M.,University of Nice Sophia Antipolis
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

Barbarians, so named after the prototype of this class (234) Barbara, are a rare class of asteroids exhibiting anomalous polarimetric properties. Their very distinctive feature is that they show negative polarization at relatively large phase angles, where all 'normal' asteroids show positive polarization. The origin of the Barbarian phenomenon is unclear, but it seems to be correlated with the presence of anomalous abundances of spinel, a mineral usually associated with the so-called calcium-aluminium-rich inclusions (CAIs) on meteorites. Since CAIs are samples of the oldest solid matter identified in our Solar system, Barbarians are very interesting targets for investigations. Inspired by the fact that some of the few known Barbarians are members of, or very close to, the dynamical family of Watsonia, we have checked whether this family is a major repository of Barbarians, in order to obtain some hints about their possible collisional origin. We have measured the linear polarization of a sample of nine asteroids which are members of the Watsonia family within the phase-angle range 17°-21°. We found that seven of them exhibit the peculiar Barbarian polarization signature, and we conclude that the Watsonia family is a repository of Barbarian asteroids. The new Barbarians identified in our analysis will be important to confirm the possible link between the Barbarian phenomenon and the presence of spinel on the surface. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ventura P.,National institute for astrophysics | D'Antona F.,National institute for astrophysics | D'Antona F.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

Lithium is made up in the envelopes of massive asymptotic giant branch (AGB) stars through the process of Hot Bottom Burning. In globular clusters, this processing is one possible source of the hot-CNO burning whose nuclear products are then ejected into the intracluster medium and take part in the formation of a second stellar generation, explaining the peculiar distribution of chemical elements among the cluster stars. We discuss the lithium yields from AGB stars in the mass range 3 to ~6.3 M⊙, and from super-AGB stars of masses in the range 6.5-9M. for metallicity Z = 10-3. The qualitative behaviour of these yields is discussed in terms of the physical structure of the different masses. Although many uncertainties affect the other yields of these stars (e.g. O, Na and Mg), even larger uncertainties affect the lithium yield, as it depends dramatically on the adopted description of mass-loss. When we adopt our standard mass-loss formulation, very large yields are obtained especially for the super-AGB stars, and we discuss their possible role on the lithium abundance of second generation stars in globular clusters. © 2010 The Authors. Journal compilation © 2009 RAS.


Larionov V.M.,Saint Petersburg State University | Villata M.,National institute for astrophysics | Raiteri C.M.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

Context: Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting in 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organised various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the analysis of this huge dataset has been the study of colour variability. Aims: The immense amount of optical and near-infrared data collected during the campaigns enables us to perform a thorough analysis of multiband data, with the aim to understand the flux variability mechanisms. Methods: We use a new approach for the analysis of these data, focusing on the source spectral evolution. Results: We show that the overall behaviour of the BL Lacertae light and colour curves can be explained in terms of a changing viewing angle of a moving, discrete emitting region, which causes variable Doppler boosting of the corresponding radiation. Conclusions: A fractal helical structure is suggested to be at the origin of the different time scales of variability. © 2010 ESO.


Corsi A.,University of Rome La Sapienza | Corsi A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Guetta D.,National institute for astrophysics | Piro L.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomy and Astrophysics | Year: 2010

Aims. We investigate whether the high energy tail detected by the Fermi/LAT for the short GRB 081024B can be caused by synchrotron and self-Compton emission in the context of either the internal or external shock models. Methods. For the internal shock scenario, we explore the possibility of generating the high energy photons directly by means of the synchrotron process, or inverse Compton emission in which target photons are synchrotron photons produced in internal shocks taking place in a lately emitted shell (delayed internal shocks). In the external shock scenario, we test whether the high energy tail can be an extension of the afterglow synchrotron emission, or alternatively the inverse Compton component associated with the afterglow synchrotron photons. Results. For the internal shock scenario, we conclude that only an inverse Compton component from delayed internal shocks can explain the high energy tail that extends to the GeV range. In the external shock scenario, we show that the high energy tail may be interpreted as synchrotron afterglow emission, if the slow cooling phase starts as early as a few seconds after the trigger. On the other hand, the observed high energy tail is consistent with an inverse Compton component of the afterglow in the fast cooling regime. © 2010 ESO.


D'Antona F.,National institute for astrophysics | Caloi V.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Ventura P.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

Core helium burning is the dominant source of energy of extreme horizontal branch stars, as the hydrogen envelope is too small to contribute to the nuclear energy output. The evolution of each mass in the HR diagram occurs along vertical tracks that, when the core helium is consumed, evolve to higher Teff and then to the white dwarf stage. The larger is the mass, the smaller is the Teff of the models, so that the zero age horizontal branch (ZAHB) is 'horizontal'. In this paper we show that, if the helium mass fraction (Y) of the envelope is larger than Y ∼ 0.5, the shape of the tracks changes completely: the hydrogen burning becomes efficient again also for very small envelope masses, thanks to the higher molecular weight and to the higher temperatures of the hydrogen shell. The larger is Y, the smaller is the envelope mass that provides strong H shell burning. These tracks have a curled shape, are located at a Teff following the approximate relation Teff = 8090 + 32900 Y and become more luminous for larger envelope masses. Consequently, the ZAHB of the very high helium models is 'vertical' in the HR diagram. Synthetic models based on these tracks nicely reproduce the location and shape of the 'blue hook' in the globular cluster ω Cen, best fit by a very high Teff (bluer) sequence with Y = 0.80 and a cooler (redder) one with Y = 0.65. Although these precise values of Y may depend on the colour-Teff conversions, we know that the helium content of the progenitors of the blue hook stars cannot be larger than Y ∼ 0.38-0.40, if they are descendants of the cluster blue main sequence. Consequently, this interpretation implies that all these objects must in fact be progeny of the blue main sequence, but they have all suffered further deep mixing, that has largely and uniformly increased their surface helium abundance, during the red giant branch evolution. A late helium flash cannot be the cause of this deep mixing, as the models we propose have hydrogen-rich envelopes much more massive than those required for a late flash. We discuss different models of deep mixing proposed in the literature, and conclude that our interpretation of the blue hook cannot be ruled out, but requires a much deeper investigation before it can be accepted. © 2010 The Authors. Journal compilation © 2010 RAS.


Kappeler F.,Karlsruhe Institute of Technology | Gallino R.,University of Turin | Gallino R.,National institute for astrophysics | Bisterzo S.,University of Turin | Aoki W.,Japan National Astronomical Observatory
Reviews of Modern Physics | Year: 2011

Nucleosynthesis in the s process takes place in the He-burning layers of low-mass asymptotic giant branch (AGB) stars and during the He- and C-burning phases of massive stars. The s process contributes about half of the element abundances between Cu and Bi in solar system material. Depending on stellar mass and metallicity the resulting s-abundance patterns exhibit characteristic features, which provide comprehensive information for our understanding of the stellar life cycle and for the chemical evolution of galaxies. The rapidly growing body of detailed abundance observations, in particular, for AGB and post-AGB stars, for objects in binary systems, and for the very faint metal-poor population represents exciting challenges and constraints for stellar model calculations. Based on updated and improved nuclear physics data for the s-process reaction network, current models are aiming at an ab initio solution for the stellar physics related to convection and mixing processes. Progress in the intimately related areas of observations, nuclear and atomic physics, and stellar modeling is reviewed and the corresponding interplay is illustrated by the general abundance patterns of the elements beyond iron and by the effect of sensitive branching points along the s-process path. The strong variations of the s-process efficiency with metallicity bear also interesting consequences for galactic chemical evolution. © 2011 American Physical Society.


Capria M.T.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Cremonese G.,National institute for astrophysics | De Sanctis M.C.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomy and Astrophysics | Year: 2010

Aims. On October 24, 2007 the comet 17P/ Holmes underwent an outburst that was extraordinary in both duration and size. We attempted to determine the cause of the outburst by acquiring and analyzing high resolution spectra of the comet. Methods. On two nights, October 25 and December 2, we acquired four high resolution spectra in the visible range at the Telescopio Nazionale Galileo in La Palma. The oxygen lines intensity ratio was estimated for the observation performed on October 25, and computed for the observation performed on December 2. Results. Many emission lines were detected in the spectra, most of them attributable to C2, NH2, CN and CH. The atomic O green line and one of the red doublet lines were detected in a spectrum acquired on October 25. All the three atomic O lines were detected in a spectrum acquired on December 2. The value obtained for the first night, 0.1 ± 0.11, implies that the H2O molecule was the main parent of the emission lines, while the value obtained for the second night, 0.3 ± 0.1, implies that the main parent was CO or CO2 instead than H2O. Conclusions. Our results imply that in the days around the outburst the water production was exceptionally high for that heliocentric distance. By December, however, the behavior of 17P/ Holmes had returned to that of a comet orbiting at 2.6 AU from the Sun, in which state the activity is probably sustained mostly by gases more volatile than water, such as CO and CO2. © 2010 ESO.


Verley S.,National institute for astrophysics | Verley S.,University of Granada | Corbelli E.,National institute for astrophysics | Giovanardi C.,National institute for astrophysics | Hunt L.K.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

Aims: In the Local Group spiral galaxy M 33, we investigate the correlation between the star formation rate (SFR) surface density, ∑SFR, and the gas density ∑gas (molecular, atomic, and total). We also explore whether there are other physical quantities, such as the hydrostatic pressure and dust optical depth, which establish a good correlation with ∑SFR. Methods: We use the Hα, far-ultraviolet (FUV), and bolometric emission maps to infer the SFR locally at different spatial scales, and in radial bins using azimuthally averaged values. Most of the local analysis is done using the highest spatial resolution allowed by gas surveys, 180 pc. The Kennicutt-Schmidt (KS) law, ∑SFR ∝ ∑ gasn is analyzed by three statistical methods. Results: At all spatial scales, with Hα emission as a SFR tracer, the KS indices n are always steeper than those derived with the FUV and bolometric emissions. We attribute this to the lack of Hα emission in low luminosity regions where most stars form in small clusters with an incomplete initial mass function at their high mass end. For azimuthally averaged values the depletion timescale for the molecular gas is constant, and the KS index is nH2 = 1.1 ± 0.1. Locally, at a spatial resolution of 180 pc, the correlation between ∑SFR and ∑gas is generally poor, even though it is tighter with the molecular and total gas than with the atomic gas alone. Considering only positions where the CO J = 1-0 line is above the 2-σ detection threshold and taking into account uncertainties in ∑H2 and ∑SFR, we obtain a steeper KS index than obtained with radial averages: nH2 = 2.22 ± 0.07 (for FUV and bolometric SFR tracers), flatter than that relative to the total gas (n Htot = 2.59 ± 0.05). The gas depletion timescale is therefore larger in regions of lower ∑SFR. Lower KS indices (nH2 = 1.46 ± 0.34 and nH2 = 1.12) are found using different fitting techniques, which do not account for individual position uncertainties. At coarser spatial resolutions these indices get slightly steeper, and the correlation improves. We find an almost linear relation and a better correlation coefficient between the local ∑SFR and the ISM hydrostatic pressure or the gas volume density. This suggests that the stellar disk, gravitationally dominant with respect to the gaseous disk in M 33, has a non-marginal role in driving the SFR. However, the tight local correlation that exists between the dust optical depth and the SFR sheds light on the alternative hypothesis that the dust column density is a good tracer of the gas that is prone to star formation. © 2010 ESO.


Pariani G.,Polytechnic of Milan | Bertarelli C.,Polytechnic of Milan | Dassa G.,Polytechnic of Milan | Bianco A.,National institute for astrophysics | Zerbi G.,Polytechnic of Milan
Optics Express | Year: 2011

The development of photochromic Computer Generated Holograms (CGHs) to test any complex optics, such as aspheres and free-form optics, is described. A thermally irreversible photochromic polyurethane has been synthesized to give good thin films with a strong modulation of the optical transmission. The photochromic CGH has been tested with a simple interferometrical configuration showing promising results. The use of photochromic CGHs provides advantages over standard technologies, as rewritability and self developing. © 2011 Optical Society of America.


Tombesi F.,NASA | Tombesi F.,University of Maryland University College | Cappi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Reeves J.N.,Keele University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

Using the results of a previous X-ray photoionizationmodelling of blueshifted Fe K absorption lines on a sample of 42 local radio-quiet AGNs observed with XMM-Newton, in this Letter we estimate the location and energetics of the associated ultrafast outflows (UFOs). Due to significant uncertainties, we are essentially able to place only lower/upper limits. On average, their location is in the interval ~0.0003-0.03 pc (~10 2-10 4r s) from the central black hole, consistent with what is expected for accretion disc winds/outflows. The mass outflow rates are constrained between ~0.01 and 1M ⊙ yr -1, corresponding to ≳ 5-10 per cent of the accretion rates. The average lower/upper limits on the mechanical power are log Ė K ≃42.6-44.6 erg s -1. However, the minimum possible value of the ratio between the mechanical power and bolometric luminosity is constrained to be comparable or higher than the minimum required by simulations of feedback induced by winds/outflows. Therefore, this work demonstrates that UFOs are indeed capable to provide a significant contribution to the AGN cosmological feedback, in agreement with theoretical expectations and the recent observation of interactions between AGN outflows and the interstellar medium in several Seyfert galaxies. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Ettori S.,National institute for astrophysics | Ettori S.,National Institute of Nuclear Physics, Italy | Molendi S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Memorie della Societa Astronomica Italiana, Supplementi - Journal of the Italian Astronomical Society, Supplement | Year: 2011

Past and current X-ray mission allow us to observe only a fraction of the volume occupied by the ICM. After reviewing the state of the art of cluster outskirts observations we discuss some important constraints that should be met when designing an experiment to measure Xray emission out to the virial radius. From what we can surmise WFXT is already designed to meet most of the requirements and should have no major diffculty in accommodating the remaining few. © SAIt 2011.


Mucciarelli A.,University of Bologna | Bellazzini M.,National institute for astrophysics | Ibata R.,University of Strasbourg | Merle T.,University of Nice Sophia Antipolis | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present the chemical analysis of 49 giant stars of the globular cluster NGC 2419, using medium resolution spectra collected with the multi-object spectrograph DEIMOS@Keck. Previous analysis of this cluster revealed a large dispersion in the line strength of the infrared Ca ii triplet, suggesting an intrinsic star-to-star scatter in its Fe or Ca content. From our analysis, we assess that all the investigated stars share the same [Fe/H], [Ca/Fe] and [Ti/Fe] abundance ratios, while a large spread in Mg and K abundances is detected. The distribution of [Mg/Fe] is bimodal, with ∼40 per cent of the observed targets having subsolar [Mg/Fe], down to [Mg/Fe] ∼ -1 dex, a level of Mg deficiency never observed before in globular clusters. It is found that the large dispersion in Mg abundances is likely the main origin of the observed dispersion of the Ca ii triplet lines strengths (that can be erroneously interpreted in terms of Fe or Ca abundance scatter) because Mg plays a relevant role in the atmosphere of giant stars as an electron donor. A strong depletion in the Mg abundance leads to an increase of the line strength of the Ca ii triplet, due to the variation in the electronic pressure, at a constant Fe and Ca abundance. Finally, we detect an anti-correlation between Mg and K abundances, not easily explainable within the framework of the current nucleosynthesis models. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Corbelli E.,National institute for astrophysics | Lorenzoni S.,National institute for astrophysics | Walterbos R.,New Mexico State University | Braun R.,CSIRO | Thilker D.,Johns Hopkins University
Astronomy and Astrophysics | Year: 2010

Aims: We test cosmological models of structure formation using the rotation curve of the nearest spiral galaxy, M31, determined using a recent deep, full-disk 21-cm imaging survey smoothed to 466 pc resolution. Methods: We fit a tilted ring model to the HI data from 8 to 37 kpc and establish conclusively the presence of a dark halo and its density distribution via dynamical analysis of the rotation curve. Results: The disk of M31 warps from 25 kpc outwards and becomes more inclined with respect to our line of sight. Newtonian dynamics without a dark matter halo provide a very poor fit to the rotation curve. In the framework of modified Newtonian dynamic (MOND) however the 21-cm rotation curve is well fitted by the gravitational potential traced by the baryonic matter density alone. The inclusion of a dark matter halo with a density profile as predicted by hierarchical clustering and structure formation in a ΛCDM cosmology makes the mass model in newtonian dynamic compatible with the rotation curve data. The dark halo concentration parameter for the best fit is C = 12 and its total mass is 1.2 × 10 12 M ⊙. If a dark halo model with a constant-density core is considered, the core radius has to be larger than 20 kpc in order for the model to provide a good fit to the data. We extrapolate the best-fit ΛCDM and constant-density core mass models to very large galactocentric radii, comparable to the size of the dark matter halo. A comparison of the predicted mass with the M31 mass determined at such large radii using other dynamical tracers, confirms the validity of our results. In particular the ΛCDM dark halo model which best fits the 21-cm data well reproduces the mass of M31 traced out to 560 kpc. Our best estimate for the total mass of M31 is 1.3 × 10 12 M ⊙, with 12% baryonic fraction and only 6% of the baryons in the neutral gas phase. © 2010 ESO.


Roche N.,University of Pennsylvania | Roche N.,National institute for astrophysics | Bernardi M.,University of Pennsylvania | Hyde J.,University of Pennsylvania
Monthly Notices of the Royal Astronomical Society | Year: 2010

We examine the colour-magnitude relation of ∼ 5000 brightest cluster galaxies (BCGs) in the Sloan Digital Sky Survey (SDSS). The colour-magnitude and colour-velocity dispersion relations of the BCGs are flatter in slope, by factors of 2 or more, than those of non-BCG early-type galaxies of similar luminosity (Mr < -22.5), while their g - r colours at the half-light radius are ∼ 0.01 mag redder.We investigate and compare radial colour gradients (which are usually negative) in these BCGs and a sample of 37 000 early-type galaxies, using a gradient estimator based on the ratio of de Vaucouleurs effective radii in g and r passbands, .reff(g)/reff(r) -1 The mean colour gradient of BCGs is flatter (by 23 per cent) than for other E/S0 galaxies of similar luminosity.The colour gradients in early-type galaxies are stronger at intermediate luminosity (Mr ≃ - 22) than at low or the highest luminosities, and tend to decrease with increasing velocity dispersion (σ). In non-BCG E/S0s, colour gradients increase for larger effective radii (up to 10-12 kpc), and are negatively correlated with 10 log σ + Mr, the mass density and stellar age. However, gradients can be reduced or inverted (positive) for post-starburst galaxies at the youngest ages. In BCGs, these trends are absent and the mean colour gradient remains at a relatively low level (∼ 0.08 by our measure) whatever the other properties of the galaxies. The redder half-light radius colours of the BCGs can be explained by their slightly greater ages combined with flatter radial colour gradients.We discuss possible explanations in terms of spheroidal galaxies initially having a colour gradient positively correlated with luminosity and positively correlated with large radius and/or low density. Subsequently, elliptical-elliptical 'dry' mergers progressively reduce colour gradients, towards a low but non-zero value. This has occurred a greater number of times during the formation histories of the most massive E/S0s, and to by far the greatest degree in the BCGs. © 2010 The Authors. Journal compilation © 2010 RAS.


Judge P.G.,High Altitude Observatory | Reardon K.,National institute for astrophysics | Cauzzi G.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2012

Narrow, thread-like structures in the Sun's chromosphere are currently understood to be plasma guided along narrow tubes of magnetic flux. We report on 1 s cadence imaging spectroscopic measurements of the Hα line with the IBIS Fabry-Pérot instrument at the Dunn Solar Telescope, obtained +0.11 nm from line center. Rapid changes grossly exceeding the Alfvén speed are commonly seen along the full extent of many chromospheric threads. We argue that only an optical superposition effect can reasonably explain the data, analogous to striations of curtains blowing in the wind. Other explanations appear to require significant contrivances to avoid contradicting various aspects of the data. We infer that the absorbing plasma exists in two-dimensional sheet-like structures within the three-dimensional magnetofluid, related perhaps to magnetic tangential discontinuities. This interpretation demands a re-evaluation of basic assumptions about low-β solar plasmas, as advocated by Parker, with broader implications in astrophysics and plasma physics. Diverse, high-cadence observations are needed to further define the relationship between magnetic field and thermal fine structure. © 2012. The American Astronomical Society. All rights reserved.


Salvaterra R.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Haardt F.,University of Insubria | Haardt F.,National Institute of Nuclear Physics, Italy | Volonteri M.,IAP | Moretti A.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

We place firm upper limits on the global accretion history of massive black holes at z > 5 from the recently measured unresolved fraction of the cosmic X-ray background. The maximum allowed unresolved intensity observed at 1.5 keV implies a maximum accreted-mass density onto massive black holes of ρ acc < 1.4 × 10 4 M Mpc -3 for z > 5. Considering the contribution of lower-z AGNs, the value reduces to ρ acc < 0.66 × 10 4 MMpc -3. The tension between the need for the efficient and rapid accretion required by the observation of massive black holes already in place at z > 7 and the strict upper limit on the accreted mass derived from the X-ray background may indicate that black holes are rare in high redshift galaxies or that accretion is only efficient for the black holes hosted by rare galaxies. © 2012 ESO.


Karhunen K.,University of Turku | Kotilainen J.K.,University of Turku | Falomo R.,National institute for astrophysics | Bettoni D.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

We study the environments of low-redshift (z<0.5) quasars based on a large and homogeneous data set from the Stripe 82 region of the Sloan Digital Sky Survey (SDSS). We have compared the<1 Mpc scale environments of 302 quasars that were resolved in our recent study to those of 288 inactive galaxies with closely matched redshifts. Crucially, the luminosities of the inactive galaxies and the quasar host galaxies are also closely matched, unlike in most previous studies. The environmental overdensities were studied by measuring the number density of galaxies within a projected distance of 200 kpc to 1Mpc. The galaxy number density of the quasar environments is comparable to that of the inactive galaxies with similar luminosities, both classes of objects showing significant excess compared to the background galaxy density for distances <400 kpc. There is no significant dependence of the galaxy number density on redshift, quasar or host galaxy luminosity, black hole mass or radio loudness. This suggests that the fuelling and triggering of the nuclear activity is only weakly dependent on the local environment of quasars, and the quasar phase may be a short-lived common phase in the life cycle of all massive galaxies. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Falomo R.,National institute for astrophysics | Bettoni D.,National institute for astrophysics | Karhunen K.,University of Turku | Kotilainen J.K.,University of Turku | Uslenghi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a photometrical and morphological study of the properties of low-redshift (z<0.5) quasars based on a large and homogeneous data set of objects derived from the Sloan Digital Sky Survey Data Release 7. This study over number by a factor of ̃5 any other previous study of quasi-stellar object (QSO) host galaxies at low redshift undertaken either on ground or on space surveys. We used ̃400 quasars that were imaged in the SDSS Stripe 82 that is up to 2 mag deeper than standard Sloan images. For these quasars we undertake a study of the host galaxies and of their environments. In this paper we report the results for the quasar hosts. We are able to detect the host galaxy for more than 3/4 of the whole data set and characterize the properties of their hosts. We found that QSO hosts are dominated by luminous galaxies of absolute magnitude M*-3 < M(R) < M*. For the unresolved objects we computed an upper limit to the host luminosity. For each well-resolved quasar we are also able to characterize the morphology of the host galaxy that turn out to be more complex than what found in previous studies. QSOs are hosted in a variety of galaxies from pure ellipticals to complex/composite morphologies that combine spheroids, disc, lens and halo. The black hole (BH) mass of the quasar, estimated from the spectral properties of the nuclei, is poorly correlated with the total luminosity of the host galaxy. However, taking into account only the bulge component we found a significant correlation between the BH mass and the bulge luminosity of the host. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bogdanov S.,Columbia University | Esposito P.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Crawford Iii F.,Franklin And Marshall College | Possenti A.,National institute for astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2014

We present X-ray observations of the "redback" eclipsing radio millisecond pulsar (MSP) and candidate radio pulsar/X-ray binary transition object PSR J1723-2837. The X-ray emission from the system is predominantly non-thermal and exhibits pronounced variability as a function of orbital phase, with a factor of 2 reduction in brightness around superior conjunction. Such temporal behavior appears to be a defining characteristic of this variety of peculiar MSP binaries and is likely caused by a partial geometric occultation by the main-sequence-like companion of a shock within the binary. There is no indication of diffuse X-ray emission from a bow shock or pulsar wind nebula associated with the pulsar. We also report on a search for point source emission and γ-ray pulsations in Fermi Large Area Telescope data using a likelihood analysis and photon probability weighting. Although PSR J1723-2837 is consistent with being a γ-ray point source, due to the strong Galactic diffuse emission at its position a definitive association cannot be established. No statistically significant pulsations or modulation at the orbital period are detected. For a presumed detection, the implied γ-ray luminosity is ≲5% of its spin-down power. This indicates that PSR J1723-2837 is either one of the least efficient γ-ray producing MSPs or, if the detection is spurious, the γ-ray emission pattern is not directed toward us. © 2014. The American Astronomical Society. All rights reserved.


Bisterzo S.,University of Turin | Gallino R.,University of Turin | Gallino R.,National institute for astrophysics | Straniero O.,National institute for astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We provide an individual analysis of 94 carbon-enhanced metal-poor stars showing an s-process enrichment (CEMP-s) collected from the literature. The s-process enhancement observed in these stars is ascribed to mass transfer by stellar winds in a binary system from a more massive companion evolving faster towards the asymptotic giant branch (AGB) phase. The theoretical AGB nucleosynthesis models have been presented in Bisterzo et al. (Paper I of this series). Several CEMP-s show an enhancement in both s- and r-process elements (CEMP-s/r). In order to explain the peculiar abundances observed in CEMP-s/r, we assume that the molecular cloud from which CEMP-s formed was previously enriched in r-elements by supernova pollution. A general discussion and the method adopted in order to interpret the observations have been provided in Bisterzo et al. (Paper II of this series). We present in this paper a detailed study of spectroscopic observations of individual stars. We consider all elements from carbon to bismuth, with particular attention to the three s-process peaks, ls (Y, Zr), hs (La, Nd, Sm) and Pb, and their ratios [hs/ls] and [Pb/hs]. The presence of an initial r-process contribution may be typically evaluated by [La/Eu]. We found possible agreements between theoretical predictions and spectroscopic data. In general, the observed [Na/Fe] (and [Mg/Fe]) provides information on the AGB initial mass, while [hs/ls] and [Pb/hs] are mainly indicators of the s-process efficiency. A range of 13C-pocket strengths are required to interpret the observations. However, major discrepancies between models and observations exist. We highlight star by star the agreements and the main problems encountered and, when possible, we suggest potential indications for further studies. These discrepancies provide starting points of debate for unsolved problems in which spectroscopic and theoretical studies may intervene. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Yue B.,Normal School of Pisa | Ferrara A.,Normal School of Pisa | Ferrara A.,University of Tokyo | Vanzella E.,National institute for astrophysics | Salvaterra R.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

By combining cosmological simulations with Frontier Field (FF) project lens models, we find that, in the most optimistic case, galaxies as faint as m ≈ 33-34 (AB magnitude at 1.6 μm) can be detected in the Frontier Fields. Such faint galaxies are hosted by dark matter haloes of mass ~109M⊙ and dominate the ionizing photon budget over currently observed bright galaxies, thus allowing for the first time the investigation of the dominant reionization sources. In addition, the observed number of these galaxies can be used to constrain the role of feedback in suppressing star formation in small haloes: for example, if galaxy formation is suppressed in haloes with circular velocity vc < 50 km s-1, galaxies fainter than m = 31 should not be detected in the FFs. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ibata R.,University of Strasbourg | Lewis G.F.,University of Sydney | Martin N.F.,University of Strasbourg | Martin N.F.,Max Planck Institute for Astronomy | And 2 more authors.
Astrophysical Journal Letters | Year: 2013

Recent analyses of the stellar stream of the Sagittarius dwarf galaxy have suggested that the kinematics and three-dimensional location of the M-giant stars in this structure constrain the dark matter halo of our Galaxy to possess a triaxial shape that is extremely flattened, being essentially an oblate ellipsoid oriented perpendicular to the Galactic disk. Using a new stream-fitting algorithm, based on a Markov Chain Monte Carlo procedure, we investigate whether this claim remains valid if we allow the density profile of the Milky Way halo greater freedom. We find stream solutions that fit the leading and trailing arms of this structure even in a spherical halo, although this would need a rising Galactic rotation curve at large Galactocentric radius. However, the required rotation curve is not ruled out by current constraints. It appears therefore that for the Milky Way, halo triaxiality, despite its strong theoretical motivation, is not required to explain the Sagittarius stream. This degeneracy between triaxiality and the halo density profile suggests that, in future endeavors to model this structure, it will be advantageous to relax the strict analytic density profiles that have been used to date. © 2013. The American Astronomical Society. All rights reserved..


Ibata R.,University of Strasbourg | Nipoti C.,Viale Berti Pichat | Sollima A.,National institute for astrophysics | Bellazzini M.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We use recently published measurements of the kinematics, surface brightness and stellarmassto- light ratio of the globular cluster NGC 2419 to examine the possibility that this Galactic halo satellite is embedded in a low-mass darkmatter halo. NGC2419 is a promising target for such a study, since its extreme Galactocentric distance and large mass would have greatly facilitated the retention of dark matter. A Markov chain Monte Carlo approach is used to investigate composite dynamical models containing a stellar and a dark matter component. We find that it is unlikely that a significant amount of dark matter (≲6 per cent of the luminous mass inside the tidal limit of the cluster) can be present if the stars follow an anisotropic Michie model and the dark matter a double power-law model. However, we find that more general models, derived using a new technique we have developed to compute non-parametric solutions to the spherical Jeans equation, suggest the presence of a significant dark matter fraction (approximately twice the stellar mass). Thus, the presence of a dark matter halo around NGC 2419 cannot be fully ruled out at present, yet any dark matter within the 10 arcmin visible extent of the cluster must be highly concentrated and cannot exceed 1.1 × 106M⊙ (99 per cent confidence), in stark contrast to expectations for a plausible progenitor halo of this structure. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Alighieri S.D.S.,National institute for astrophysics | Finelli F.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Finelli F.,National Institute of Nuclear Physics, Italy | Galaverni M.,National Institute of Nuclear Physics, Italy
Astrophysical Journal | Year: 2010

We report on an update of the test on the rotation of the plane of linear polarization for light traveling over cosmological distances, using a comparison between the measured direction of the UV polarization in eight radio galaxies at z>2 and the direction predicted by the model of scattering of anisotropic nuclear radiation, which explains the polarization. No rotation is detected within a few degrees for each galaxy and, if the rotation does not depend on direction, then the all-sky-average rotation is constrained to be θ = -0.°8 ± 2°.2. We discuss the relevance of this result for constraining cosmological birefringence when this is caused by the interaction with a cosmological pseudo-scalar field or by the presence of a Cherns-Simons term. © 2010. The American Astronomical Society. All rights reserved.


Baykal A.,METU - MEMS Center | Gougus E.,Sabanci University | Ionam S.C.,Ankara University | Belloni T.,National institute for astrophysics
Astrophysical Journal | Year: 2010

We present the discovery of the orbital period of Swift J1626.6-5156. Since its discovery in 2005, the source has been monitored with Rossi X-Ray Timing Explorer, especially during the early stage of the outburst and into the X-ray modulating episode. Using a data span of 700 days, we obtain the orbital period of the system as 132.9 days. We find that the orbit is close to a circular shape with an eccentricity 0.08, that is one of the smallest among Be/X-ray binary systems. Moreover, we find that the timescale of the X-ray modulations varied, which led to earlier suggestions of orbital periods at about a third and half of the orbital period of Swift J1626.6-5156. © 2010 The American Astronomical Society.


Vazza F.,Jacobs University Bremen | Vazza F.,National institute for astrophysics | Bruggen M.,Jacobs University Bremen | Gheller C.,Swiss National Supercomputing Center | Brunetti G.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present a numerical scheme, implemented in the cosmological adaptive mesh refinement code enzo, to model the injection of cosmic ray (CR) particles at shocks, their advection and their dynamical feedback on thermal baryonic gas. We give a description of the algorithms and show their tests against analytical and idealized one-dimensional problems. Our implementation is able to track the injection of CR energy, the spatial advection of CR energy and its feedback on the thermal gas in run-time. This method is applied to study CR acceleration and evolution in cosmological volumes, with both fixed and variable mesh resolution. We compare the properties of galaxy clusters with and without CRs for a sample of high-resolution clusters with different dynamical states. At variance with similar simulations based on smoothed particles hydrodynamics, we report that the inclusion of CR feedback in our method decreases the central gas density in clusters, thus reducing the X-ray and Sunyaev-Zeldovich effect from the clusters centre, while enhancing the gas density and its related observables near the virial radius. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Corsi A.,University of Rome La Sapienza | Corsi A.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Corsi A.,California Institute of Technology | Guetta D.,National institute for astrophysics | Piro L.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astrophysical Journal | Year: 2010

We investigate the origin of the prompt and delayed emission observed in the short GRB 090510. We use the broadband data to test whether the most popular theoretical models for gamma-ray burst emission can accommodate the observations for this burst. We first attempt to explain the soft-to-hard spectral evolution associated with the delayed onset of a GeV tail with the hypothesis that the prompt burst and the high-energy tail both originate from a single process, namely, synchrotron emission from internal shocks (IS). Considerations on the compactness of the source imply that the high-energy tail should be produced in a late-emitted shell, characterized by a Lorentz factor greater than the one generating the prompt burst. However, in this hypothesis, the predicted evolution of the synchrotron peak frequency does not agree with the observed soft-to-hard evolution. Given the difficulties of a single-mechanism hypothesis, we test two alternative double-component scenarios. In the first, the prompt burst is explained as synchrotron radiation from IS and the high-energy emission (up to about 1 s following the trigger) as IS synchrotron-self-Compton. In the second scenario, in view of its long duration (∼100 s), the high-energy tail is decoupled from the prompt burst and has an external shock origin. In this case, we show that a reasonable choice of parameters does indeed exist to accommodate the optical-to-GeV data, provided the Lorentz factor of the shocked shell is sufficiently high. Finally, we attempt to explain the chromatic break observed around ∼103 s with a structured jet model. We find that this might be a viable explanation and that it lowers the high value of the burst energy derived by assuming isotropy, ∼1053 erg, below ∼1049 erg, which is more compatible with the energetics from a binary merger progenitor. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


Schneider R.,National institute for astrophysics | Omukai K.,Kyoto University | Limongi M.,National institute for astrophysics | Ferrara A.,Normal School of Pisa | And 3 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

The relative importance of metals and dust grains in the formation of the first low-mass stars has been a subject of debate. The recently discovered Galactic halo star SDSS J102915+172927 has a mass less than 0.8M and a metallicity of Z = 4.5 × 10-5 Z. We investigate the origin and properties of this star by reconstructing the physical conditions in its birth cloud. We show that the observed elemental abundance trend of SDSS J102915+172927 can be well fitted by the yields of core-collapse supernovae (SNe) with metal-free progenitors of 20 and 35M. Using these selected SN explosion models, we compute the corresponding dust yields and the resulting dust depletion factor taking into account the partial destruction by the SN reverse shock. We then follow the collapse and fragmentation of a star-forming cloud enriched by the products of these SN explosions at the observed metallicity of SDSS J102915+172927. We find that 0.05-0.1M mass fragments, which then lead to the formation of low-mass stars, can occur provided that the mass fraction of dust grains in the birth cloud exceeds 0.01 of the total mass of metals and dust. This, in turn, requires that at least 0.4M of dust condense in the first SNe, allowing for moderate destruction by the reverse shock. If dust formation in the first SNe is less efficient or strong dust destruction does occur, the thermal evolution of the SDSS J102915+172927 birth cloud is dominated by molecular cooling, and only ≥8M fragments can form. We conclude that the observed properties of SDSS J102915+172927 support the suggestion that dust must have condensed in the ejecta of the first SNe and played a fundamental role in the formation of the first low-mass stars. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society. © 2012 RAS.


Portinari L.,University of Turku | Kotilainen J.,University of Turku | Falomo R.,National institute for astrophysics | Decarli R.,University of Insubria | Decarli R.,Max Planck Institute for Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2012

Quasars are useful tracers of the cosmological evolution of the black hole mass-galaxy relation. We compare the expectations of semi-analytical models (SAMs) of galaxy evolution to the largest available data sets of quasar host galaxies out to z≃ 3. Observed quasar hosts are consistent with no evolution from the local M BH-L host relation and suggest a significant increase of the mass ratio from z= 0 to 3. Taken at face value, this is totally at odds with the predictions of SAMs, where the intrinsic Γ shows little evolution and quasar host galaxies at high redshift are systematically overluminous (and/or have an undermassive BH). However, since quasars preferentially trace very massive black holes (10 9-10 10M ⊙) at the steep end of the luminosity and mass function, the ensuing selection biases can reconcile the present SAMs with the observations. A proper interpretation of quasar host data thus requires the global approach of SAMs so as to account for statistical biases. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Bianco A.,National institute for astrophysics | Perissinotto S.,Italian Institute of Technology | Garbugli M.,Polytechnic of Milan | Lanzani G.,Italian Institute of Technology | And 2 more authors.
Laser and Photonics Reviews | Year: 2011

In this work studies on photochromism for optics and photonics are reviewed. The versatility of organic chemistry gives photochromic materials wide opportunities for several applications that range from tunable filters and gratings, to refractive-index modulators for optical fibers and communications, to optical memories and sensors. Moreover, novel results on amplified emission efficient modulation in a conjugated polymer/photochromic system are presented. The versatility of organic chemistry gives photochromic materials wide opportunities for several applications that range from tunable filters and gratings, to refractive-index modulators for optical fibers and communications, to optical memories and sensors. In this work studies on photochromism for photonics are reviewed. Moreover, novel results on amplified emission efficient modulation in a conjugated polymer/photochromic system are presented. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Blasi P.,National institute for astrophysics | Blasi P.,National Institute of Nuclear Physics, Italy | Amato E.,National institute for astrophysics | Serpico P.D.,University of Savoy
Physical Review Letters | Year: 2012

We show that the complex shape of the cosmic ray (CR) spectrum, as recently measured by PAMELA and inferred from Fermi-LAT γ-ray observations of molecular clouds in the Gould belt, can be naturally understood in terms of basic plasma astrophysics phenomena. A break from a harder to a softer spectrum at rigidity R≃10GV follows from a transition from transport dominated by advection of particles with Alfvén waves to a regime where diffusion in the turbulence generated by the same CRs is dominant. A second break at R≃200GV happens when the diffusive propagation is no longer determined by the self-generated turbulence, but rather by the cascading of externally generated turbulence (for instance due to supernova bubbles) from large spatial scales to smaller scales where CRs can resonate. Implications of this scenario for the cosmic ray spectrum, grammage, and anisotropy are discussed. © 2012 American Physical Society.


Maio U.,National institute for astrophysics | Maio U.,Leibniz Institute for Astrophysics Potsdam | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present results of cosmological N-body hydrodynamic chemistry simulations of primordial structure growth and evolution in a scenario with warm dark matter (WDM) having a mass of 3 keV (thermal relic) and compare with a model consisting of standard cold dark matter (CDM).We focus on the high-redshift universe (z > 6), where the structure formation process should better reflect the primordial (linear) differences in terms of matter power spectrum. We find that early epochs can be exceptional probes of the dark matter nature. Non-linear WDM power spectra and mass functions are up to 2 dex lower than in CDM and show spreads of factor of a few persisting in the whole first Gyr. Runaway molecular cooling in WDM haloes results severely inhibited because of the damping of power at large k modes and hence cosmic (Populations III and II-I) star formation rate (SFR) is usually suppressed with respect to CDM predictions. Luminous objects formed in a WDM background are very rare at z > 10, due to the sparser and retarded evolution of early WDM minihaloes during the dark ages and their lack can be fitted with a simple analytical formula depending only on magnitude and redshift. Future high-z observations of faint galaxies have the potential to discriminate between CDM and WDM scenarios by means of cosmic stellar mass density and specific SFR, as well. When compared to the effects of alternative cosmologies (e.g. non-Gaussian or dark energy models) or of high-order corrections at large z (e.g. primordial streaming motions or changes in the pristine initial mass function) the ones caused by WDM are definitely more dramatic. © 2014 The Authors.


Bisterzo S.,University of Turin | Gallino R.,University of Turin | Gallino R.,National institute for astrophysics | Straniero O.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

High-resolution spectroscopic observations of 100 metal-poor carbon and s-rich stars (CEMP-s) collected from the literature are compared with the theoretical nucleosynthesis models of the asymptotic giant branch (AGB) presented in Paper I (MAGB ini= 1.3, 1.4, 1.5, 2 M⊙, - 3.6 ≲ [ Fe/H ] ≲- 1.5). The s-process enhancement detected in these objects is associated with binary systems: the more massive companion evolved faster through the thermally pulsing AGB phase (TP-AGB), synthesizing s-elements in the inner He intershell, which are partly dredged up to the surface during the third dredge-up (TDU) episode. The secondary observed low-mass companion became CEMP-s by the mass transfer of C- and s-rich material from the primary AGB. We analyse the light elements C, N, O, Na and Mg, as well as the two s-process indicators, [hs/ls] (where ls =〈Y,Zr〉 is the the light-s peak at N = 50 and hs =〈La,Nd,Sm〉 the heavy-s peak at N = 82) and [Pb/hs]. We distinguish between CEMP-s with high s-process enhancement, [hs/Fe] >rsim 1.5 (CEMP-sII), and mild s-process enhanced stars, [hs/Fe] < 1.5 (CEMP-sI). To interpret the observations, a range of s-process efficiencies at any given metallicity is necessary. This is confirmed by the high spread observed in [Pb/hs] (∼2dex). A degeneration of solutions is found with some exceptions: most main-sequence CEMP-sII stars with low [Na/Fe] can only be interpreted with MAGB ini= 1.3-1.4M⊙. Giants having suffered the first dredge-up (FDU) need a dilution >rsim1dex (dil is defined as the mass of the convective envelope of the observed star, Mobs {black star}, over the material transferred from the AGB to the companion, Mtrans AGB). Then AGB models with higher AGB initial masses (MAGB ini= 1.5-2M⊙) are adopted to interpret CEMP-sII giants. In general, solutions with AGB models in the mass range MAGB ini= 1.3-2M⊙ and different dilution factors are found for CEMP-sI stars. About half of the CEMP-s stars with europium measurements show a high r-process enhancement (CEMP-s/r). The scenario for the origin of CEMP-s/r stars is a debated issue. We propose that the molecular cloud from which the binary system formed was previously enriched in r-process elements, most likely by local SNII pollution. This initial r-enrichment does not affect the s-process nucleosynthesis. However, for a high r-process enrichment ([r/Fe]ini= 2) the r-process contributions to solar La, Nd and Sm (30, 40 and 70 per cent) have to be considered. This increases the maximum [hs/ls] up to ∼0.3dex. CEMP-s/r stars reflect this behaviour, showing higher [hs/ls] than observed in CEMP-s on average. Detailed analyses for individual stars will be provided in Paper III. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Aurass H.,Leibniz Institute for Astrophysics Potsdam | Mann G.,Leibniz Institute for Astrophysics Potsdam | Zlobec P.,National institute for astrophysics | Karlicky M.,Academy of Sciences of the Czech Republic
Astrophysical Journal | Year: 2011

We reconsider the 2003 October 28 X17 flare/coronal mass ejection (CME), studying the five minutes immediately before the impulsive flare phase (not discussed in previous work). To this aim we examine complementary dynamic radio spectrograms, single frequency polarimeter records, radio images, space-based longitudinal field magnetograms, and ultraviolet images. We find widely distributed faint and narrowband meter wave radio sources located outside active regions but associated with the boundaries of magnetic flux connectivity cells, inferred from the potential extrapolation of the observed photospheric longitudinal field as a model for coronal magnetic field structures. The meter wave radio sources occur during the initial decimeter wave effects, which are well known to be associated with filament destabilization in the flaring active region (here NOAA 10486). Antiochos etal. predict in their break-out model for CME initiation that "... huge phenomena ... may be controlled by detailed plasma processes that occur in relatively tiny regions." They suggest that the expected faint energy release "... on long field lines far away from any neutral line ... may be detectable in radio/microwave emission from nonthermal particles..." In this paper, we describe meter wave sources whose properties correctly coincide with the quoted predictions of the break-out reconnection model of the CME initiation. © 2011. The American Astronomical Society. All rights reserved.


Bellazzini M.,National institute for astrophysics | Dalessandro E.,University of Bologna | Sollima A.,National institute for astrophysics | Ibata R.,University of Strasbourg
Monthly Notices of the Royal Astronomical Society | Year: 2012

We used archival Hubble Space Telescope Wide Field Camera 3 (WFC3) images to obtain the luminosity function of the remote globular cluster NGC 2419 from 2 mag above the horizontal branch level down to ≃ 3.0 mag below the turn-off point (to M I≃ 6.4), approximately covering the range of initial stellar masses The completeness-corrected luminosity function does not display any change of shape over the radial range covered by the WFC3 data, out to ≃ 6 core radii (r c), or, equivalently, to ≃ 2 half-light radii. The luminosity function in this radial range is also identical to that obtained from ground-based data at much larger distances from the cluster centre (), in the magnitude range in which the two distributions overlap (M I≤ 4.0). These results support the conclusion by Dalessandro et al. that there is no significant mass segregation among cluster stars; hence, the stellar mass-to-light ratio remains constant with distance from the cluster centre. We fitted the observed luminosity function with theoretical counterparts with the proper age and metallicity from different sets of stellar evolution models, and we consistently derive a total V-band mass-to-light ratio by extrapolating to the hydrogen-burning limit, with a best-fitting value M/L V= 1.5 ± 0.1. On the other hand, assuming that there are no cluster stars with m≤ 0.3M ⊙, we establish a robust lower limit M/L V > 0.8. These estimates provide useful constraints for dynamical models of the cluster that were forced to consider the stellar mass-to-light ratio as a (nearly) free parameter. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Giocoli C.,National institute for astrophysics | Giocoli C.,National Institute of Nuclear Physics, Italy | Tormen G.,University of Padua | Sheth R.K.,Abdus Salam International Center For Theoretical Physics | Sheth R.K.,University of Pennsylvania
Monthly Notices of the Royal Astronomical Society | Year: 2012

We develop a simple model for estimating the mass growth histories of dark matter haloes. The model is based on a fit to the formation time distribution, where formation is defined as the earliest time that the main branch of the merger tree contains a fraction f of the final mass M. Our analysis exploits the fact that the median formation time as a function of f is the same as the median of the main progenitor mass distribution as a function of time. When coupled with previous work showing that the concentration c of the final halo is related to the formation time t f associated with f∼ 0.04, our approach provides a simple algorithm for estimating how the distribution of halo concentrations may be expected to depend on mass, redshift and the expansion history of the background cosmology. We also show that one can predict log 10c with a precision of about 0.13 and 0.09 dex if only its mass or both mass and t f are known. Moreover, conversely, one can predict log 10t f from mass or c with a precision of 0.12 and 0.09 dex, approximately independent of f. Adding the mass to the c-based estimate does not result in further improvement. These latter results may be useful for studies which seek to compare the age of the stars in the central galaxy in a halo with the time the core was first assembled. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Novakovic B.,University of Belgrade | Hsieh H.H.,University of Hawaii at Manoa | Cellino A.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2012

In this paper, we apply different methods to examine the possibility that a small group of 24 asteroids dynamically linked to a main-belt comet P/2006 VW 139, recently discovered by the Pan-STARRS1 survey telescope, shares a common physical origin. By applying the hierarchical clustering and backward integration methods, we find strong evidence that 11 of these asteroids form a sub-group which likely originated in a recent collision event, and that this group includes P/2006 VW 139. The objects not found to be part of the 11-member sub-group, which we designate as the P/2006 VW 139 family, were either found to be dynamically unstable or are likely interlopers which should be expected due to the close proximity of the Themis family. As we demonstrated, statistical significance of the P/2006 VW 139 family is >99per cent. We determine the age of the family to be 7.5 ± 0.3Myr, and estimate the diameter of the parent body to be ∼11km. Results show that the family is produced by an impact which can be best characterized as a transition from the catastrophic to the cratering regime. The dynamical environment of this family is studied as well, including the identification of the most influential mean motion and secular resonances in the region. Our findings now make P/2006 VW 139 the second main-belt comet to be dynamically associated with a young asteroid family, a fact with important implications for the origin and activation mechanism of such objects. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Biazzo K.,National institute for astrophysics | D'Orazi V.,Macquarie University | D'Orazi V.,Monash University | Desidera S.,National institute for astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present stellar parameters and abundances of 11 elements (Li, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni and Zn) of 13 F6-K2 main-sequence stars in the young groups AB Doradus, Carina Near and Ursa Major. The exoplanet-host star ι Horologii is also analysed. The three young associations have lithiumabundance consistent with their age. All other elements show solar abundances. The three groups are characterized by a small scatter in all abundances, with mean [Fe/H] values of 0.10 (s = 0.03), 0.08 (σ = 0.05) and 0.01 (σ =0.03) dex for AB Doradus, Carina Near and Ursa Major, respectively. The distribution of elemental abundances appears congruent with the chemical pattern of the Galactic thin disc in the solar vicinity, as found for other young groups. This means that the metallicity distribution of nearby young stars, targets of direct-imaging planet-search surveys, is different from that of old, field solar-type stars, i.e. the typical targets of radial velocitysurveys. The young planet-host star ι Horologii shows a lithium abundance lower than that found for the young association members. It is found to havea slightly super-solar iron abundance ([Fe/H] = 0.16±0.09), while all [X/Fe] ratios are similar to the solar values. Its elemental abundances are close to those of the Hyades cluster derived from the literature, which seemsto reinforce the idea of a possible common origin with the primordial cluster. © 2012 The Authors.


Ayala A.,University of Granada | Dominguez I.,University of Granada | Giannotti M.,Barry University | Mirizzi A.,University of Hamburg | Straniero O.,National institute for astrophysics
Physical Review Letters | Year: 2014

We derive a strong bound on the axion-photon coupling gaγ from the analysis of a sample of 39 Galactic Globular Clusters. As recognized long ago, the R parameter, i.e., the number ratio of stars in horizontal over red giant branch of old stellar clusters, would be reduced by the axion production from photon conversions occurring in stellar cores. In this regard, we have compared the measured R with state-of-the-art stellar models obtained under different assumptions for gaγ. We show that the estimated value of gaγ substantially depends on the adopted He mass fraction Y, an effect often neglected in previous investigations. Taking as a benchmark for our study the most recent determinations of the He abundance in H ii regions with O/H in the same range of the Galactic Globular Clusters, we obtain an upper bound gaγ<0.66×10-10GeV-1 at 95% confidence level. This result significantly improves the constraints from previous analyses and is currently the strongest limit on the axion-photon coupling in a wide mass range. © 2014 American Physical Society.


Benitez A.D.,National institute for astrophysics | Casillas J.,University of Granada
Soft Computing | Year: 2013

When we face a problem with a high number of variables using a standard fuzzy system, the number of rules increases exponentially and the obtained fuzzy system is scarcely interpretable. This problem can be handled by arranging the inputs in hierarchical ways. This paper presents a multi-objective genetic algorithm that learns serial hierarchical fuzzy systems with the aim of coping with the curse of dimensionality. By means of an experimental study, we have observed that our algorithm obtains good results in interpretability and accuracy with problems in which the number of variables is relatively high. © 2012 Springer-Verlag.


Bisterzo S.,University of Turin | Gallino R.,University of Turin | Straniero O.,National institute for astrophysics | Cristallo S.,University of Granada | Kappeler F.,Karlsruhe Institute of Technology
Monthly Notices of the Royal Astronomical Society | Year: 2010

A large sample of carbon-enhanced metal-poor stars enriched in s-process elements (CEMP-s) have been observed in the Galactic halo. These stars of low mass (M∼ 0.9 M⊙) are located on the main-sequence or the red-giant phase, and do not undergo third dredge-up (TDU) episodes. The s-process enhancement is most plausibly due to accretion in a binary system from a more massive companion when on the asymptotic giant branch (AGB) phase (now a white dwarf). In order to interpret the spectroscopic observations, updated AGB models are needed to follow in detail the s-process nucleosynthesis. We present nucleosynthesis calculations based on AGB stellar models obtained with Frascati Raphson-Newton Evolutionary Code (franec) for low initial stellar masses and low metallicities. For a given metallicity, a wide spread in the abundance of the s-process elements is obtained by varying the amount of 13C and its profile in the pocket, where the 13C(α, n)16O reaction is the major neutron source, releasing neutrons in radiative conditions during the interpulse phase. We also account for the second neutron source 22Ne(α, n)25Mg, partially activated during convective thermal pulses. We discuss the surface abundance of elements from carbon to bismuth, for AGB models of initial masses M = 1.3-2 M⊙, low metallicities ([Fe/H] from -1 down to -3.6) and for different 13C-pocket efficiencies. In particular, we analyse the relative behaviour of the three s-process peaks: light-s (ls at magic neutron number N = 50), heavy-s (hs at N = 82) and lead (N = 126). Two s-process indicators, [hs/ls] and [Pb/hs], are needed in order to characterize the s-process distribution. In the on-line material, we provide a set of data tables with surface predictions. Our final objective is to provide a full set of theoretical models of low-mass low-metallicity s-process-enhanced stars. In a forthcoming paper, we will test our results through a comparison with observations of CEMP-s stars. © 2010 The Authors. Journal compilation © 2010 RAS.


Camera S.,University of Lisbon | Cardone V.F.,National institute for astrophysics | Radicella N.,University of Salerno
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Alterations of the gravity Lagrangian introduced in modified torsion gravity theories - also referred to as f(T) gravity - allows for an accelerated expansion in a matter-dominated Universe. In this framework, the cosmic speed-up is driven by an effective "torsion fluid." Besides the background evolution of the Universe, structure formation is also modified because of a time-dependent effective gravitational constant. Here, we investigate the imprints of f(T) gravity on galaxy clustering and weak gravitational lensing to the aim of understanding whether future galaxy surveys could constrain torsion gravity and discriminate between it and standard general relativity. Specifically, we compute Fisher matrix forecasts for two viable f(T) models to both infer the accuracy on the measurement of the model parameters and evaluate the power that a combined clustering and shear analysis will have as a tool for model selection. We find that with such a combination of probes it will indeed be possible to tightly constrain f(T) model parameters. Moreover, the Occam's razor provided by the Bayes factor will allow us to confirm an f(T) power-law extension of the concordance ΛCDM model, if a value larger than 0.02 of its power-law slope were measured, whereas in ΛCDM it is exactly 0. © 2014 American Physical Society.


Coradini A.,National institute for astrophysics | Magni G.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Turrini D.,National institute for astrophysics
Space Science Reviews | Year: 2010

The subject of satellite formation is strictly linked to the one of planetary formation. Giant planets strongly shape the evolution of the circum-planetary disks during their formation and thus, indirectly, influence the initial conditions for the processes governing satellite formation. In order to fully understand the present features of the satellite systems of the giant planets, we need to take into account their formation environments and histories and the role of the different physical parameters. In particular, the pressure and temperature profiles in the circum-planetary nebulae shaped their chemical gradients by allowing for the condensation of ices and noble gases. These chemical gradients, in turn, set the composition of the satellitesimals, which represent the building blocks of the present regular satellites. © 2010 Springer Science+Business Media B.V.


Bartels-Rausch T.,Paul Scherrer Institute | Bergeron V.,Ecole Normale Superieure de Lyon | Cartwright J.H.E.,University of Granada | Escribano R.,CSIC - Institute for the Structure of Matter | And 13 more authors.
Reviews of Modern Physics | Year: 2012

From the frontiers of research on ice dynamics in its broadest sense, this review surveys the structures of ice, the patterns or morphologies it may assume, and the physical and chemical processes in which it is involved. Open questions in the various fields of ice research in nature are highlighted, ranging from terrestrial and oceanic ice on Earth, to ice in the atmosphere, to ice on other Solar System bodies and in interstellar space. © 2012 American Physical Society.


Spitoni E.,University of Évora | Matteucci F.,National institute for astrophysics | Marcon-Uchida M.M.,Southern Cross University of Brazil
Astronomy and Astrophysics | Year: 2013

Context. Galactic fountains and radial gas flows are very important ingredients for modeling the chemical evolution of galactic disks. Aims. Our aim here is to study the effects of galactic fountains and radial gas flows on the chemical evolution of the disk of Andromeda (M 31) galaxy. Methods. We adopt a ballistic method to study the effects of galactic fountains on the chemical enrichment of the M 31 disk by analyzing the landing coordinate of the fountains and the time delay in the pollution of the interstellar gas. To understand the consequences of radial flows, we adopt a very detailed chemical evolution model. Our aim is to study the formation of abundance gradients along the M 31 disk and also compare our results with the Milky Way. Results. We find that the landing coordinate for the fountains in M 31 is no more than 1 kpc from the starting point, thus producing a negligible effect on the chemical evolution of the disk. We find that the delay time in the enrichment process due to fountains is no longer than 100 Myr, and this timescale also produces insignificant effects on the results. Then, we compute the chemical evolution of the M 31 disk with radial gas flows produced by the infall of extragalactic material and fountains. We find that a moderate inside-out formation of the disk, coupled with radial flows of variable speed, can reproduce the observed gradient very well. We also discuss the effects of other parameters, such as a threshold in the gas density for star formation and efficiency of star formation varying with the galactic radius. Conclusions. We conclude that galactic fountains do not affect the chemical evolution of the M 31 disk. Including radial gas flows with an inside-out formation of the disk produces a very good agreement with observations. On the other hand, if radial flows are not considered, one should assume a threshold in the star formation and variable star formation efficiency, besides the inside-out formation to reproduce the data. We conclude that the most important physical processes in creating disk gradients are the inside-out formation and the radial gas flows. More data on abundance gradients both locally and at high redshift are necessary to confirm this conclusion. © ESO, 2013.


Stiele H.,National institute for astrophysics | Belloni T.M.,National institute for astrophysics | Kalemci E.,Sabanci University | Motta S.,European Space Agency
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present a study of correlations between spectral and timing parameters for a sample of black hole X-ray binary candidates. Data are taken from GX339-4, H1743-322 and XTE J1650-500, as the Rossi X-ray Timing Explorer observed complete outbursts of these sources. In our study we investigate outbursts that happened before the end of 2009 to make use of the high-energy coverage of the High Energy X-ray Timing Experiment detector and select observations that show a certain type of quasi-periodic oscillations (QPOs; type-C). The spectral parameters are derived using the empirical convolution model SIMPL to model the Comptonized component of the emission together with a disc blackbody for the emission of the accretion disc. Additional spectral features, namely a reflection component, a high-energy cut-off and excess emission at 6.4 keV, are taken into account. Our investigations confirm the known positive correlation between photon index and centroid frequency of the QPOs and reveal an anticorrelation between the fraction of up-scattered photons and the QPO frequency. We show that both correlations behave as expected in the 'sombrero' geometry. Furthermore, we find that during outburst decay the correlation between photon index and QPO frequency follows a general track, independent of individual outbursts. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Spitoni E.,University of Trieste | Spitoni E.,University of Évora | Matteucci F.,University of Trieste | Matteucci F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2011

Context. The majority of chemical evolution models assume that the Galactic disk forms by means of infall of gas and divide the disk into several independent rings without exchange of matter between them. However, if gas infall is important, radial gas flows should be taken into account as a dynamical consequence of infall. Aims. We test the effects of radial gas flows on detailed chemical evolution models (one-infall and two-infall) of the Milky Way disk with different prescriptions for the infall law and star formation rate. Methods. We modified the equation of chemical evolution to include radial gas flows according to the method described in Portinari & Chiosi (2000, A&A, 355, 929). Results. We found that with a gas radial inflow of constant speed the metallicity gradient tends to steepen. Taking into account a constant timescale for the infall rate along the Galaxy disk and radial flows with a constant speed, we obtained too flat a gradient, at variance with data, implying that an inside-out formation and/or a variable gas flow speed are required. To explain the observed gradients, the gas flow should increase in modulus with the galactocentric distance, in both the one-infall and two-infall models. However, the inside-out disk formation coupled with a threshold in the gas density (only in the two-infall model) for star formation and/or a variable efficiency of star formation with galactocentric distance can also reproduce the observed gradients without radial flows. Conclusions. We show that the radial flows can be the most important process in reproducing abundance gradients but only with a variable gas speed. Finally, one should consider that uncertainties in the data concerning gradients prevent us from drawing firm conclusions. Future more detailed data will help us to ascertain whether the radial flows are a necessary ingredient in the formation and evolution of the Galactic disk and disks in general. © 2011 ESO.


Bonaldi A.,National institute for astrophysics | Ricciardi S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Monthly Notices of the Royal Astronomical Society | Year: 2011

We investigate the detectability of the primordial cosmic microwave background (CMB) polarization B-mode power spectrum on large scales in the presence of instrumental noise and realistic foreground contamination. We have worked out a method to estimate the errors on component separation and to propagate them up to the power spectrum estimation. The performance of our method is illustrated by applying it to the instrumental specifications of the Planck satellite and to the proposed configuration for the next-generation CMB polarization experiment COrE. We demonstrate that a proper component separation step is required in order to achieve the detection of B-modes on large scales and that the final sensitivity to B-modes of a given experiment is determined by a delicate balance between the noise level and the residual foregrounds, which depend on the set of frequencies exploited in the CMB reconstruction, on the signal-to-noise ratio of each frequency map and on our ability to correctly model the spectral behaviour of the foreground components. We have produced a flexible software tool that allows a comparison of performances on B-mode detection of different instrumental specifications (choice of frequencies, noise level at each frequency, etc.) as well as of different proposed approaches to component separation. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Caloi V.,Istituto di Astrofisica Spaziale e Fisica Cosmica | D'Antona F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011

The vast majority of globular clusters so far examined shows the chemical signatures of hosting (at least) two stellar populations. According to recent ideas, this feature requires a two-step process, in which the nuclearly processed matter from a 'first generation' (FG) of stars gives birth to a 'second generation' (SG), bearing the fingerprint of a fully carbon-nitrogen-oxygen (CNO) cycled matter. Since, as observed, the present population of most globular clusters is made up largely of SG stars, a substantial fraction of the FG (≳90 per cent) must be lost. Nevertheless, two types of clusters dominated by a simple stellar population (FG clusters) should exist: clusters initially too small to be able to retain a cooling flow and form a second generation (FG-only clusters) and massive clusters that could retain the CNO-processed ejecta and form an SG, but were unable to lose a significant fraction of their FG (mainly-FG clusters). Identification of mainly-FG clusters may provide an estimate of the fraction of the initial mass involved in the formation of the SG. We attempt a first classification of FG clusters, based on the morphology of their horizontal branches (HBs), as displayed in the published catalogues of photometric data for 106 clusters. We select, as FG candidates, the clusters in which the HB can be reproduced by the evolution of an almost unique mass. We find that less than 20 per cent of clusters with [Fe/H] < -0.8 appear to be FG, but only ∼10 per cent probably had a mass sufficient to form at all an SG. This small percentage confirms on a wider data base the spectroscopic result that the SG is a dominant constituent of today's clusters, suggesting that its formation is an ingredient necessary for the survival of globular clusters during their dynamical evolution in the Galactic tidal field. In more detail we show that Pal 3 turns out to be a good example of FG-only cluster. Instead, HB simulations and space distribution of its components indicate that M53 is a 'mainly-FG' cluster that evolved in dynamic isolation and developed a small SG in its core thanks to its large mass. Mainly-FG candidates may also be NGC 5634, NGC 5694 and NGC 6101. In contrast, NGC 2419 contains >30 per cent of SG stars, and its present dynamical status bears less information on its formation process than the analysis of the chemical abundances of its stars and of its HB morphology. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


D'Orazi V.,Macquarie University | D'Orazi V.,Monash University | Campbell S.W.,Monash University | Lugaro M.,Monash University | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Globular clusters display significant variations in their light-element content, pointing to the existence of a second stellar generation formed from the ejecta of an earlier generation. The nature of these internal polluters is still a matter of debate: the two most popular scenarios indicate intermediate-mass asymptotic giant branch (IM-AGB) stars and fast rotating massive stars. Abundances determination for some key elements can help distinguish between these competitor candidates. We present in this paper Y abundances for a sample of 103 red giant branch stars in NGC 6121. Within measurement errors, we find that the [Y/Fe] is constant in this cluster contrary to a recent suggestion. For a subsample of six stars we also find [Rb/Fe] to be constant, consistent with previous studies showing no variation in other s-process elements. We also present a new set of stellar yields for IM-AGB stellar models of 5 and 6M⊙, including heavy element s-process abundances. The uncertainties on the mass-loss rate, the mixing length parameter and the nuclear reaction rates have a major impact on the stellar abundances. Within the IM-AGB pollution scenario, the constant abundance of heavy elements inside the cluster requires a marginal s-process efficiency in IM-AGB stars. Such a constrain could still be satisfied by the present models assuming a stronger mass-loss rate. The uncertainties mentioned above are limiting the predictive power of IM-AGB models. For these reasons, at the moment we are not able to clearly rule out their role as main polluters of the second population stars in globular clusters. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Catanzaro G.,National institute for astrophysics | Ripepi V.,National institute for astrophysics | Bruntt H.,University of Aarhus
Monthly Notices of the Royal Astronomical Society | Year: 2013

In this paper, we present a detailed spectroscopic analysis of the suspected marginal Am star HD 71297. Our goal is to test the accuracy of two different approaches to determine the atmospheric parameters: effective temperature, gravity, projected rotational velocity and chemical abundances. The methods used in this paper are: classical spectral synthesis and the Versatile Wavelength Analysis (VWA) software. Since our star is bright and very close to the Sun, we were able to determine its effective temperature and gravity directly through photometric, interferometric and parallax measurements. The values found were taken as reference to which we compare the values derived by spectroscopic methods. Our analysis leads us to conclude that the spectroscopic methods considered in this study to derive fundamental parameters give consistent results, if we consider all the sources of experimental errors, that have been discussed in the text. In addition, our study shows that the spectroscopic results are quite as accurate as those derived from direct measurements. As for the specific object analysed here, according to our analysis, HD 71297 has chemical abundances not compatible with the previous spectral classification. We found moderate underabundances of carbon, sodium, magnesium and iron-peak elements, while oxygen, aluminium, silicon, sulphur and heavy elements (Z ≥ 39) are solar in content. This chemical pattern has been confirmed by the calculations performed with both methods.© 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ghizzardi S.,Istituto di Astrofisica Spaziale e Fisica Cosmica | De Grandi S.,National institute for astrophysics | Molendi S.,Istituto di Astrofisica Spaziale e Fisica Cosmica
Astronomische Nachrichten | Year: 2013

Cold-fronts in cool-core clusters are thought to be induced by minor mergers and to develop through a sloshing mechanism. While temperature and surface-brightness jumps have been detected and measured in many systems, a detailed characterization of the metal abundance across the discontinuity is only available for a handful of objects. Within the sloshing scenario, we expect the central cool and metal rich gas to be displaced outwards into lower abundance regions, thus generating a metal discontinuity across the front. We analyzed a long (120 ks) XMM-Newton observation of A496 to study the metal distribution and its correlation with the cold-fronts. We find Fe discontinuities across the two main cold-fronts located ~ 60 kpc NNW and ~ 160 kpc south of the peak and a metal excess in the south direction. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Marcha M.J.M.,University of Lisbon | Caccianiga A.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013

This paper presents a new sample of BL Lac objects selected from a deep (30 mJy) radio survey of flat spectrum radio sources (the CLASS blazar survey). The sample is one of the largest well-defined samples in the low-power regime with a total of 130 sources of which 55 satisfy the 'classical' optical BL Lac selection criteria, and the rest have indistinguishable radio properties. The primary goal of this study is to establish the radio luminosity function (RLF) on firm statistical ground at low radio luminosities where previous samples have not been able to investigate. The gain of taking a peek at lower powers is the possibility to search for the flattening of the luminosity function which is a feature predicted by the beaming model but which has remained elusive to observational confirmation. In this study, we extend for the first time the BL Lac RLF down to very low radio powers ~ 1022 WHz-1, i.e. two orders of magnitude below the RLF currently available in the literature. In the process, we confirm the importance of adopting a broader, and more physically meaningful set of classification criteria to avoid the systematic missing of low-luminosity BL Lacs. Thanks to the good statistics we confirm the existence of weak but significant positive cosmological evolution for the BL Lac population, and we detect, for the first time the flattening of the RLF at L ~ 1025 WHz-1 in agreement with the predictions of the beaming model. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Ibata R.,University of Strasbourg | Sollima A.,National institute for astrophysics | Nipoti C.,University of Bologna | Bellazzini M.,National institute for astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2011

We present the analysis of a kinematic data set of stars in the globular cluster NGC2419, taken with the DEep Imaging Multi-Object Spectrograph at the Keck II telescope. Combined with a reanalysis of deep Hubble Space Telescope and Subaru Telescope imaging data, which provide an accurate luminosity profile of the cluster, we investigate the validity of a large set of dynamical models of the system, which are checked for stability via N-body simulations. We find that isotropic models in either Newtonian or Modified Newtonian Dynamics (MOND) are ruled out with extremely high confidence. However, a simple Michie model in Newtonian gravity with anisotropic velocity dispersion provides an excellent representation of the luminosity profile and kinematics of the cluster. The anisotropy profiles of these models ensure an isotropic center to the cluster, which progresses to extreme radial anisotropy toward the outskirts. In contrast, with MOND we find that Michie models that reproduce the luminosity profile either overpredict the velocity dispersion on the outskirts of the cluster if the mass-to-light ratio (M/L) is kept at astrophysically motivated values or else they underpredict the central velocity dispersion if the M/L is taken to be very small. We find that the best Michie model in MOND is a factor of 10 4 less likely than the Newtonian model that best fits the system. A likelihood ratio of 350 is found when we investigate more general models by solving the Jeans equation with a Markov Chain Monte Carlo scheme. We verified with N-body simulations that these results are not significantly different when the MOND external field effect is accounted for. If the assumptions that the cluster is in dynamical equilibrium, spherical, not on a peculiar orbit, and possesses a single dynamical tracer population of constant M/L are correct, we conclude that the present observations provide a very severe challenge for MOND. © 2011. The American Astronomical Society. All rights reserved.


Vazza F.,Jacobs University Bremen | Vazza F.,National institute for astrophysics | Bruggen M.,Jacobs University Bremen | Gheller C.,Swiss National Supercomputing Center
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate the observable effects of feedback from active galactic nuclei (AGN) on nonthermal components of the intracluster medium (ICM). We have modelled feedback from AGN in cosmological simulations with the adaptive mesh refinement code ENZO, investigating three types of feedback that are sometimes called quasar, jet and radio mode. Using a small set of galaxy clusters simulated at high resolution, we model the injection and evolution of cosmic rays, as well as their effects on the thermal plasma. By comparing both the profiles of thermal gas to observed profiles from the ACCEPT sample and the secondary γ -ray emission to the available upper limits from Fermi, we discuss how the combined analysis of these two observables can constrain the energetics and mechanisms of feedback models in clusters. Those modes of AGN feedback that provide a good match to X-ray observations yield a γ -ray luminosity resulting from secondary cosmic rays that is about 10 times below the available upper limits from Fermi. Moreover, we investigate the injection of turbulent motions into the ICM from AGN, and the detectability of these motions via the analysis of line broadening of the Fe XXIII line. In the near future, deeper observations/upper limits of non-thermal emissions from galaxy clusters will yield stringent constraints on the energetics and modes of AGN feedback, even at early cosmic epochs. © 2012 The Authors.


Tombesi F.,NASA | Tombesi F.,University of Maryland University College | Cappi M.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Reeves J.N.,Keele University | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

The existence of ionized X-ray absorbing layers of gas along the line of sight to the nuclei of Seyfert galaxies is a well established observational fact. This material is systematically outflowing and shows a large range in parameters. However, its actual nature and dynamics are still not clear. In order to gain insights into these important issues we performed a literature search for papers reporting the parameters of the soft X-ray warm absorbers (WAs) in 35 type 1 Seyferts and compared their properties to those of the ultra-fast outflows (UFOs) detected in the same sample. The fraction of sources with WAs is >60 per cent, consistent with previous studies. The fraction of sources with UFOs is >34 per cent, >67 per cent of which also show WAs. The large dynamic range obtained when considering all the absorbers together, spanning several orders of magnitude in ionization, column, velocity and distance allows us, for the first time, to investigate general relations among them. In particular, we find significant correlations indicating that the closer the absorber is to the central black hole, the higher the ionization, column, outflow velocity and consequently the mechanical power. In all the cases, the absorbers continuously populate the whole parameter space, with the WAs and the UFOs lying always at the two ends of the distribution. These evidence strongly suggest that these absorbers, often considered of different types, could actually represent parts of a single large-scale stratified outflow observed at different locations from the black hole. The UFOs are likely launched from the inner accretion disc and the WAs at larger distances, such as the outer disc and/or torus. We argue that the observed parameters and correlations are, to date, consistent with both radiation pressure through Compton scattering and magnetohydrodynamic processes contributing to the outflow acceleration, the latter playing a major role. Most of the absorbers, especially the UFOs, show a sufficiently high mechanical power (at least ∼0.5 per cent of the bolometric luminosity) to provide a significant contribution to active galactic nuclei (AGN) feedback and thus to the evolution of the host galaxy. In this regard, we find possible evidence for the interaction of the AGN wind with the surrounding environment on large scales. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Cowley C.R.,University of Michigan | Castelli F.,National institute for astrophysics | Hubrig S.,Leibniz Institute for Astrophysics Potsdam
Monthly Notices of the Royal Astronomical Society | Year: 2013

The double-lined spectroscopic binary HD 104237 (DX Cha) is part of a complex system of some half-dozen nearby young stars. We report a significant change from an orbit for the SB2 system derived from 1999-2000 observations. We obtain abundances from the primary and secondary spectra. The abundance analysis uses both detailed spectral synthesis and determinations based on equivalent widths of weak absorption lines withWλ typically<25 mÅ. Abundances are derived for 25 elements in the primary, and 17 elements in the secondary. Apart from lithium and zirconium, abundances do not depart significantly from solar. Lithium may be marginally enhanced with respect to the meteoritic value in the primary. It somewhat depleted in the secondary. The emission-line spectrum is typical of Herbig Ae stars. We compare and contrast the spectra of the HD 104237 primary and two other Herbig Ae stars with low v sin (i), HD 101412 and HD 190073. © 2013 The AuthorsPublished by Oxford University Press on behalf of the Royal Astronomical Society.


Gerard J.-C.,University of Liège | Soret L.,University of Liège | Piccioni G.,National institute for astrophysics | Drossart P.,Observatoire de Paris Meudon
Icarus | Year: 2014

Images of the nightside limb of Venus have been obtained in the northern hemisphere with the VIRTIS multispectral infrared imager on board Venus Express between April 2006 and October 2008. We analyze the latitudinal distribution of the O2(a1δ) airglow limb profiles at 1.27μm to characterize its distribution and variability. We show that the instantaneous structure of the emission is very different from the statistical global view of an enhanced emission near the equator, decreasing in brightness and slightly increasing in altitude toward the poles. The peak intensity of the limb profiles varies by a factor up to 50 between the brightest spots and the darkest regions. The bright airglow spots correspond to regions of enhanced downward flow of oxygen atoms originating from the dayside. Considerable variations in brightness and morphology are observed in the altitude-latitudinal distribution over a 24-h period. Analysis of the limb profiles indicates that secondary airglow peaks located at altitudes higher than the mean value of 96km are observed on about 30% of the latitudinal cuts, but they are concentrated in narrow latitude areas extending over a few hundred kilometers. Most of them occur in transition regions between two altitude regimes in the 50° to 60°N region, possibly associated with the drop of the cloud top altitude observed equatorward of the "cold collar". We interpret these results as an indication that the strength of vertical transport in this mesosphere-thermosphere transition region is very variable both in location and time. This variability, also observed in nadir airglow images and wind measurements, is a key characteristic of the mesosphere-thermosphere transition region. It may be caused by fluctuations of the global day-to-night circulation generated by gravity waves. We show with a one-dimensional model that local enhancements of eddy transport is a possibility. This variability is currently not accounted for by global circulation models that predict a single stable region of enhanced airglow in the vicinity of the antisolar point. © 2014 Elsevier Inc.


Bertarelli C.,Polytechnic of Milan | Bertarelli C.,Italian Institute of Technology | Bianco A.,National institute for astrophysics | Castagna R.,Polytechnic of Milan | And 3 more authors.
Journal of Photochemistry and Photobiology C: Photochemistry Reviews | Year: 2011

Opportunities to apply photochromism in smart optics are highlighted. The reversible light-triggered switching in UV-vis absorption and in the refractive index can be exploited to develop rewritable optical elements, specifically tunable masks, amplitude holograms and volume gratings. Description of the configuration and performance of the optical devices with possible open issues is preceded by a discussion dealing with the molecular features that provide a strong modulation of the material properties which is required for a convenient functioning of the device. © 2011 Elsevier B.V.


Correnti M.,University of Bologna | Bellazzini M.,National institute for astrophysics | Ibata R.A.,University of Strasbourg | Ferraro F.R.,University of Bologna | Varghese A.,University of Strasbourg
Astrophysical Journal | Year: 2010

We trace the tidal Stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Red Clump (RC) stars from the catalog of the Sloan Digital Sky Survey-Data Release 6, in the range 150° ≲ R.A. ≲ 220°, corresponding to the range of orbital azimuth 220° ≲ Λ ≲ 290°. Substructures along the line of sight (los) are identified as significant peaks in the differential star count profiles (SCPs) of candidate RC stars. A proper modeling of the SCPs allows us to obtain (1) ≤ 10% accurate, purely differential distances with respect to the main body of Sgr, (2) estimates of the FWHM along the los, and (3) estimates of the local density, for each detected substructure. In the range 255° ≲ Λ ≲ 290° we cleanly and continuously trace various coherent structures that can be ascribed to the Stream, in particular: the well-known northern portion of the leading arm, running from d ≃ 43 kpc at Λ ≃ 290° to d ≃ 30 kpc at Λ ≃ 255°, and a more nearby coherent series of detections lying at a constant distance d ≃ 25 kpc, that can be identified with a wrap of the trailing arm. The latter structure, predicted by severalmodels of the disruption of Sgr dSph, was never traced before; comparison with existing models indicates that the difference in distance between these portions of the leading and trailing arms may provide a powerful tool to discriminate between theoretical models assuming different shapes of the Galactic potential. A further, more distant wrap in the same portion of the sky is detected only along a couple of los. For Λ ≲ 255° the detected structures are more complex and less easily interpreted. We are confident of being able to trace the continuation of the leading arm down to Λ ≃ 220° and d ≃ 20 kpc; the trailing arm is seen up to Λ ≃ 240° where it is replaced by more distant structures. Possible detections of more nearby wraps and of the Virgo Stellar Stream are also discussed. These measured properties provide a coherent set of observational constraints for the next generation of theoretical models of the disruption of Sgr. © 2010. The American Astronomical Society. All rights reserved.


Risaliti G.,National institute for astrophysics | Risaliti G.,Harvard - Smithsonian Center for Astrophysics | Imanishi M.,Japan National Astronomical Observatory | Sani E.,University of Florence
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present a quantitative estimate of the relative active galactic nucleus (AGN)/starburst content in a sample of 59 nearby (z < 0.15) infrared bright ultraluminous infrared galaxies (ULIRGs) taken from the 1-Jy sample, based on infrared L-band (3-4 μm) spectra. By using diagnostic diagrams and a simple deconvolution model, we show that at least 60 per cent of local ULIRGs contain an active nucleus, but the AGN contribution to the bolometric luminosity is relevant only in ∼15-20 per cent of the sources. Overall, ULIRGs appear to be powered by the starburst process, responsible for >85 per cent of the observed infrared luminosity. The subsample of sources optically classified as low-ionization nuclear emission-line regions (LINERs; 31 objects) shows a similar AGN/starburst distribution as the whole sample, indicating a composite nature for this class of objects. We also show that a few ULIRGs, optically classified as starbursts, have L-band spectral features suggesting the presence of a buried AGN. © 2009 RAS.


Bruno R.,National institute for astrophysics | Trenchi L.,National institute for astrophysics | Telloni D.,Dell
Astrophysical Journal Letters | Year: 2014

We investigated the behavior of the spectral slope of interplanetary magnetic field fluctuations at proton scales for selected high-resolution time intervals from the WIND and MESSENGER spacecraft at 1 AU and 0.56 AU, respectively. The analysis was performed within the profile of high-speed streams, moving from fast to slow wind regions. The spectral slope showed a large variability between -3.75 and -1.75 and a robust tendency for this parameter to be steeper within the trailing edge, where the speed is higher, and to be flatter within the subsequent slower wind, following a gradual transition between these two states. The value of the spectral index seems to depend firmly on the power associated with the fluctuations within the inertial range; the higher the power, the steeper the slope. Our results support previous analyses suggesting that there must be some response of the dissipation mechanism to the level of the energy transfer rate along the inertial range. © 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


Bodo G.,National institute for astrophysics | Cattaneo F.,University of Chicago | Mignone A.,University of Turin | Rossi P.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2014

We consider the problem of convergence in stratified isothermal shearing boxes with zero net magnetic flux. We present results with the highest resolution to date - up to 200 grid points per pressure scale height - that show no clear evidence of convergence. Rather, the Maxwell stresses continue to decrease with increasing resolution. We propose some possible scenarios to explain the lack of convergence based on multi-layer dynamo systems. © 2014. The American Astronomical Society. All rights reserved..


Valiante R.,National institute for astrophysics | Schneider R.,National institute for astrophysics | Maiolino R.,University of Cambridge | Salvadori S.,NOVA Kapteyn Astronomical Institute | Bianchi S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

Galaxy-scale gas outflows triggered by active galactic nuclei have been proposed as a key physical process to regulate the co-evolution of nuclear black holes and their host galaxies. The recent detection of a massive gas outflowin one of the most distant quasars, SDSS J1148+5251 at z = 6.4, presented by Maiolino et al., strongly supports this idea and suggests that strong quasar feedback is already at work at very early times. In a previous work, Valiante et al., we have presented a hierarchical semi-analytical model, GAMETE/QSODUST, for the formation and evolution of high-redshift quasars, and we have applied it to the quasar SDSS J1148+5251, with the aim of investigating the star formation history, the nature of the dominant stellar populations and the origin and properties of the large dust mass observed in the host galaxy. A robust prediction of the model is that the evolution of the nuclear black hole and of the host galaxy are tightly coupled by quasar feedback in the form of strong galaxy-scale winds. In the present Letter, we show that the gas outflow rate predicted by GAMETE/QSODUST is in good agreement with the lower limit of 3500M ⊙ yr -1 inferred by the observations. According to the model, the observed outflow at z=6.4 is dominated by quasar feedback, as the outflow rate has already considerably depleted the gas content of the host galaxy, leading to a downturn in the star formation rate at z < 7-8. Hence, we predict that supernova explosions give a negligible contribution to the observed winds at z = 6.4. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society © 2012 RAS.


La Barbera F.,National institute for astrophysics | Ferreras I.,University College London | de Carvalho R.R.,National Institute for Space Research | Bruzual G.,National Autonomous University of Mexico | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

Radial trends of stellar populations in galaxies provide a valuable tool to understand the mechanisms of galaxy growth. In this paper, we present the first comprehensive analysis of optical-optical and optical-NIR colours, as a function of galaxy mass, out to the halo region (8R e) of early-type galaxies (ETGs). We select a sample of 674 massive ETGs (M *≳ 3 × 10 10M Ȯ) from the Sloan Digital Sky Survey (SDSS)-based SPIDER survey. By comparing with a large range of population synthesis models, we derive robust constraints on the radial trends in age and metallicity. Metallicity is unambiguously found to decrease outwards, with a measurable steepening of the slope in the outer regions (R e > R > 8R e). The gradients in stellar age are found to be more sensitive to the models used, but in general, the outer regions of ETGs feature older populations compared to the cores. This trend is strongest for the most massive galaxies in our sample (M *≳ 10 11Ṁ). Furthermore, when segregating with respect to large-scale environment, the age gradient is more significant in ETGs residing in higher density regions. These results shed light on the processes leading from the formation of the central core to the growth of the stellar envelope of massive galaxies. The fact that the populations in the outer regions are older and more metal-poor than in the core suggests a process whereby the envelope of massive galaxies is made up of accreted small satellites (i.e. minor mergers) whose stars were born during the first stages of galaxy formation. © 2012 The Authors Monthly Notices of the Royal Astronomical Society.


Landi E.,University of Michigan | Reale F.,University of Palermo | Reale F.,National institute for astrophysics | Testa P.,Smithsonian Astrophysical Observatory
Astronomy and Astrophysics | Year: 2012

Context. Recent studies carried out with SOHO and Hinode high-resolution spectrometers have shown that the plasma in the off-disk solar corona is close to isothermal. If confirmed, these findings may have significant consequences for theoretical models of coronal heating. However, these studies have been carried out with diagnostic techniques whose ability to reconstruct the plasma distribution with temperature has not been thoroughly tested. Aims. In this paper, we carry out tests on the Monte Carlo Markov chain (MCMC) technique with the aim of determining: 1) its ability to retrieve isothermal plasmas from a set of spectral line intensities, with and without random noise; 2) to what extent can it discriminate between an isothermal solution and a narrow multithermal distribution; and 3) how well it can detect multiple isothermal components along the line of sight. We also test the effects of 4) atomic data uncertainties on the results, and 5) the number of ions whose lines are available for the DEM reconstruction. Methods. We first use the CHIANTI database to calculate synthetic spectra from different thermal distributions: single isothermal plasmas, multithermal plasmas made of multiple isothermal components, and multithermal plasmas with a Gaussian DEM distribution with variable width. We then apply the MCMC technique on each of these synthetic spectra, so that the ability of the MCMC technique at reconstructing the original thermal distribution can be evaluated. Next, we add a random noise to the synthetic spectra, and repeat the exercise, in order to determine the effects of random errors on the results. We also we repeat the exercise using a different set of atomic data from those used to calculate synthetic line intensities, to understand the robustness of the results against atomic physics uncertainties. The size of the temperature bin of the MCMC reconstruction is varied in all cases, in order to determine the optimal width. Results. We find that the MCMC technique is unable to retrieve isothermal plasmas to better than Δlog T ≈ 0.05. Also, the DEM curves obtained using lines calculated with an isothermal plasma and with a Gaussian distribution with FWHM of log T ≈ 0.05 are very similar. Two near-isothermal components can be resolved if their temperature separation is Δlog T = 0.2 or larger. Thus, DEM diagnostics has an intrinsic resolving power of log T = 0.05. Atomic data uncertainties may significantly affect both temperature and peak DEM values, but do not alter our conclusions. The availability of small sets of lines also does not worsen the performance of the MCMC technique, provided these lines are formed in a wide temperature range. Conclusions. Our analysis shows the present limitations in our ability to identify the presence of strictly isothermal plasmas in stellar and solar coronal spectra. © 2012 ESO.


Regis M.,University of Turin | Xia J.-Q.,CAS Institute of High Energy Physics | Cuoco A.,University of Turin | Branchini E.,Third University of Rome | And 4 more authors.
Physical Review Letters | Year: 2015

If dark matter (DM) is composed by particles which are nongravitationally coupled to ordinary matter, their annihilations or decays in cosmic structures can result in detectable radiation. We show that the most powerful technique to detect a particle DM signal outside the Local Group is to study the angular cross-correlation of nongravitational signals with low-redshift gravitational probes. This method allows us to enhance the signal to noise from the regions of the Universe where the DM-induced emission is preferentially generated. We demonstrate the power of this approach by focusing on GeV-TeV DM and on the recent cross-correlation analysis between the 2MASS galaxy catalogue and the Fermi-LAT γ-ray maps. We show that this technique is more sensitive than other extragalactic γ-ray probes, such as the energy spectrum and angular autocorrelation of the extragalactic background, and emission from clusters of galaxies. Intriguingly, we find that the measured cross-correlation can be well fitted by a DM component, with a thermal annihilation cross section and mass between 10 and 100 GeV, depending on the small-scale DM properties and γ-ray production mechanism. This solicits further data collection and dedicated analyses. © 2015 American Physical Society.


Pallottini A.,Normal School of Pisa | Ferrara A.,Normal School of Pisa | Ferrara A.,University of Tokyo | Gallerani S.,Normal School of Pisa | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We study cosmic metal enrichment via adaptive mesh refinement hydrodynamical simulations in a (10 Mpc h-1)3 volume following the Population III (PopIII)-PopII transition and for different PopIII initial mass function (IMFs). We have analysed the joint evolution of metal enrichment on galactic and intergalactic scales at z = 6 and z = 4. Galaxies account for ≳9 per cent of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density (Δ ≳ 1), (b) the true intergalactic medium (IGM, 1 < Δ ≳ 10) and (c) the circumgalactic medium (CGM, 10 < Δ ≳ 102.5), the interface between the IGM and galaxies. At z = 6, a galactic mass-metallicity relation is established. At z = 4, galaxies with a stellar mass M* ≃ 108.5M⊙ show log(O/H) + 12 = 8.19, consistent with observations. The total amount of heavy elements rises from ωSFH Z = 1.52 × 10-6 at z=6 to 8.05 × 10-6 at z = 4. Metals in galaxies make up to ≃0.89 of such budget at z = 6; this fraction increases to ≃0.95 at z = 4. At z = 6 (z = 4), the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z = 4 a density-metallicity (Δ-Z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z ~ 10-3.5 Z⊙ in the CGM, Z steeply rises with density up to ≃10-2 Z⊙. In all diffuse phases, a considerable fraction of metals is in a warm/hot (T μ-1 > 104.5 K) state. Due to these physical conditions, CIV absorption line experiments can probe only ≃2 per cent of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the PopIII star formation history is almost insensitive to the chosen PopIII IMF. PopIII stars are preferentially formed in truly pristine (Z = 0) gas pockets, well outside polluted regions created by previous star formation episodes. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bernardini F.,Wayne State University | Bernardini F.,National institute for astrophysics | Cackett E.M.,Wayne State University
Monthly Notices of the Royal Astronomical Society | Year: 2014

We conducted the first long-term (75 d) X-ray monitoring of the black hole low-mass X-ray binary V404 Cyg, with the goal of understanding and characterizing its variability during quiescence. The X-ray light curve of V404 Cyg shows several flares on time-scales of hours with a count rate change of a factor of about 5-8. The root-mean-square variability is Fvar = 57.0 ± 3.2 per cent. The first-order structure function is consistent with both a power spectrum of index -1 (flicker noise), or with a power spectrum of index 0 (white noise), implying that the light curve is variable on time-scales from days to months. The X-ray spectrum is well fitted by a power law with spectral index τ = 2.10-2.35, and we found that the spectral shape remains roughly constant as the flux changes. A constant spectral shape with respect to a change in the X-ray flux may favour a scenario in which the X-ray emission is dominated by synchrotron radiation produced in a jet. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Waizmann J.-C.,University of Bologna | Waizmann J.-C.,National institute for astrophysics | Waizmann J.-C.,National Institute of Nuclear Physics, Italy | Redlich M.,University of Heidelberg | Bartelmann M.,University of Heidelberg
Astronomy and Astrophysics | Year: 2012

Context. With the amount and quality of galaxy cluster data increasing, the question arises whether or not the standard cosmological model can be questioned on the basis of a single observed extreme galaxy cluster. Usually, the word extreme refers directly to cluster mass, which is not a direct observable and thus subject to substantial uncertainty. Hence, it is desirable to extend studies of extreme clusters to direct observables, such as the Einstein radius. Aims. We aim to evaluate the occurrence probability of the large observed Einstein radius of MACS J0717.5+3745 within the standard ΛCDM cosmology. In particular, we want to model the distribution function of the single largest Einstein radius in a given cosmological volume and to study which underlying assumptions and effects have the strongest impact on the results. Methods. We obtain this distribution by a Monte Carlo approach, based on the semi-analytic modelling of the halo population on the past lightcone. After sampling the distribution, we fit the results with the general extreme value (GEV) distribution which we use for the subsequent analysis. Results. We find that the distribution of the maximum Einstein radius is particularly sensitive to the precise choice of the halo mass function, lens triaxiality, the inner slope of the halo density profile and the mass-concentration relation. Using the distributions so obtained, we study the occurrence probability of the large Einstein radius of MACS J0717.5+3745, finding that this system is not in tension with ΛCDM. We also find that the GEV distribution can be used to fit very accurately the sampled distributions and that all of them can be described by a (type-II) Fréchet distribution. Conclusions. With a multitude of effects that strongly influence the distribution of the single largest Einstein radius, it is more than doubtful that the standard ΛCDM cosmology can be ruled out on the basis of a single observation. If, despite the large uncertainties in the underlying assumptions, one wanted to do so, a much larger Einstein radius (≳ 100″) than that of MACS J0717.5+3745 would have to be observed. © 2012 ESO.


Redlich M.,University of Heidelberg | Bartelmann M.,University of Heidelberg | Waizmann J.-C.,University of Bologna | Waizmann J.-C.,National institute for astrophysics | And 2 more authors.
Astronomy and Astrophysics | Year: 2012

For more than a decade now, it has been controversial whether or not the high rate of giant gravitational arcs and the largest observed Einstein radii are consistent with the standard cosmological model. Recent studies indicate that mergers provide an efficient mechanism to substantially increase the strong-lensing efficiency of individual clusters. Based on purely semi-analytic methods, we investigated the statistical impact of cluster mergers on the distribution of the largest Einstein radii and the optical depth for giant gravitational arcs of selected cluster samples. Analysing representative all-sky realizations of clusters at redshifts z < 1 and assuming a constant source redshift of zs = 2:0, we find that mergers increase the number of Einstein radii above 10′′ (20′′) by ∼35% (∼55%). Exploiting the tight correlation between Einstein radii and lensing cross sections, we infer that the optical depth for giant gravitational arcs with a length-to-width ratio ≥7:5 of those clusters with Einstein radii above 10′′ (20′′) increases by ∼45% (∼85%). Our findings suggest that cluster mergers significantly influence in particular the statistical lensing properties of the strongest gravitational lenses. We conclude that semi-analytic studies must inevitably take these events into account before questioning the standard cosmological model on the basis of the largest observed Einstein radii and the statistics of giant gravitational arcs. © 2012 ESO.


Prokhorov D.A.,Stanford University | Colafrancesco S.,University of Witwatersrand | Colafrancesco S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

Clusters of galaxies are mainly formed by merging of smaller structures, according to the standard cosmological scenario. If the mass of a substructure is>10 per cent of that of a galaxy cluster, the temperature distribution of the intracluster medium (ICM) in a merging cluster becomes inhomogeneous. Various methods have been used to derive the two-dimensional projected temperature distribution of the ICM. However, methods for studying temperature distribution along the line of sight through the cluster were absent. In this Letter, we present the first measurement of the temperature standard deviation along the line of sight, using as a reference case the multifrequency Sunyaev-Zel'dovich measurements of the Bullet Cluster. We find that the value of the temperature standard deviation is high and equals to (10.6 ± 3.8) keV in the Bullet Cluster. This result shows that the temperature distribution in the Bullet Cluster is strongly inhomogeneous along the line ofsight and provides a new method for studying galaxy clusters in depth. © 2012 The Authors, MNRAS 424, L49-L53 Monthly Notices of the Royal Astronomical Society. © 2012 RAS.


Salmi F.,University Paris Diderot | Daddi E.,University Paris Diderot | Elbaz D.,University Paris Diderot | Sargent M.T.,University Paris Diderot | And 4 more authors.
Astrophysical Journal Letters | Year: 2012

Using a mass-limited sample of 24 μm detected, star-forming galaxies at 0.5 < z < 1.3, we study the mass-star formation rate (SFR) correlation and its tightness. The correlation is well defined (σ = 0.28dex) for disk galaxies (n Sérsic < 1.5), while more bulge-dominated objects often have lower specific SFRs (sSFRs). For disk galaxies, a much tighter correlation (σ = 0.19dex) is obtained if the rest-frame H-band luminosity is used instead of stellar mass derived from multi-color photometry. The sSFR correlates strongly with rest-frame optical colors (hence luminosity-weighted stellar age) and also with clumpiness (which likely reflects the molecular gas fraction). This implies that most of the observed scatter is real, despite its low level, and not dominated by random measurement errors. After correcting for these differential effects a remarkably small dispersion remains (σ = 0.14dex), suggesting that measurement errors in mass or SFR are ≲ 0.10dex, excluding systematic uncertainties. Measurement errors in stellar masses, the thickening of the correlation due to real sSFR variations, and varying completeness with stellar mass, can spuriously bias the derived slope to lower values due to the finite range over which observables (mass and SFR) are available. When accounting for these effects, the intrinsic slope for the main sequence for disk galaxies gets closer to unity. © 2012. The American Astronomical Society. All rights reserved.


Correnti M.,US Space Telescope Science Institute | Goudfrooij P.,US Space Telescope Science Institute | Kalirai J.S.,US Space Telescope Science Institute | Kalirai J.S.,University of Baltimore | And 3 more authors.
Astrophysical Journal | Year: 2014

We use the Wide Field Camera 3 on board the Hubble Space Telescope (HST) to obtain deep, high-resolution images of two intermediate-age star clusters in the Large Magellanic Cloud of relatively low mass (104M ⊙) and significantly different core radii, namely NGC 2209 and NGC 2249. For comparison purposes, we also reanalyzed archival HST images of NGC 1795 and IC 2146, two other relatively low-mass star clusters. From the comparison of the observed color-magnitude diagrams with Monte Carlo simulations, we find that the main-sequence turnoff (MSTO) regions in NGC 2209 and NGC 2249 are significantly wider than that derived from simulations of simple stellar populations, while those in NGC 1795 and IC 2146 are not. We determine the evolution of the clusters' masses and escape velocities from an age of 10 Myr to the present age. We find that differences among these clusters can be explained by dynamical evolution arguments if the currently extended clusters (NGC 2209 and IC 2146) experienced stronger levels of initial mass segregation than the currently compact ones (NGC 2249 and NGC 1795). Under this assumption, we find that NGC 2209 and NGC 2249 have estimated escape velocities, V esc≳ 15 km s-1at an age of 10 Myr, large enough to retain material ejected by slow winds of first-generation stars, while the two clusters that do not feature extended MSTOs have V esc≲ 12 km s-1at that age. These results suggest that the extended MSTO phenomenon can be better explained by a range of stellar ages rather than a range of stellar rotation velocities or interacting binaries. © 2014. The American Astronomical Society. All rights reserved..


Mignone A.,University of Turin | Zanni C.,National institute for astrophysics | Tzeferacos P.,University of Turin | Van Straalen B.,Lawrence Berkeley National Laboratory | And 2 more authors.
Astrophysical Journal, Supplement Series | Year: 2012

We present a description of the adaptive mesh refinement (AMR) implementation of the PLUTO code for solving the equations of classical and special relativistic magnetohydrodynamics (MHD and RMHD). The current release exploits, in addition to the static grid version of the code, the distributed infrastructure of the CHOMBO library for multidimensional parallel computations over block-structured, adaptively refined grids. We employ a conservative finite-volume approach where primary flow quantities are discretized at the cell center in a dimensionally unsplit fashion using the Corner Transport Upwind method. Time stepping relies on a characteristic tracing step where piecewise parabolic method, weighted essentially non-oscillatory, or slope-limited linear interpolation schemes can be handily adopted. A characteristic decomposition-free version of the scheme is also illustrated. The solenoidal condition of the magnetic field is enforced by augmenting the equations with a generalized Lagrange multiplier providing propagation and damping of divergence errors through a mixed hyperbolic/parabolic explicit cleaning step. Among the novel features, we describe an extension of the scheme to include non-ideal dissipative processes, such as viscosity, resistivity, and anisotropic thermal conduction without operator splitting. Finally, we illustrate an efficient treatment of point-local, potentially stiff source terms over hierarchical nested grids by taking advantage of the adaptivity in time. Several multidimensional benchmarks and applications to problems of astrophysical relevance assess the potentiality of the AMR version of PLUTO in resolving flow features separated by large spatial and temporal disparities. © 2012. The American Astronomical Society. All rights reserved.


Testa P.,Smithsonian Astrophysical Observatory | Reale F.,University of Palermo | Reale F.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2012

We use coronal imaging observations with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), and Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) spectral data to explore the potential of narrowband EUV imaging data for diagnosing the presence of hot (T ≳ 5MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging and EIS spectral data, including the Ca XVII line (at 192.8Å), which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful co-alignment of the imaging and spectral data, we compare the morphology in a three-color image combining the 171, 335, and 94Å AIA spectral bands, with the image obtained for Ca XVII emission from the analysis of EIS spectra. We find that in the selected active regions the Ca XVII emission is strong only in very limited areas, showing striking similarities with the features bright in the 94Å (and 335Å) AIA channels and weak in the 171Å band. We conclude that AIA imaging observations of the solar corona can be used to track hot plasma (6-8MK), and so to study its spatial variability and temporal evolution at high spatial and temporal resolution. © 2012. The American Astronomical Society. All rights reserved.


Travaglio C.,National institute for astrophysics | Ropke F.K.,University of Würzburg | Ropke F.K.,Max Planck Institute for Astrophysics | Gallino R.,National institute for astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2011

Beyond Fe, there is a class of 35 proton-rich nuclides, between 74Se and 196Hg, called p-nuclei. They are bypassed by the s and r neutron capture processes and are typically 10-1000times less abundant than the s- and/or r-isotopes in the solar system. The bulk of p-isotopes is created in the "gamma processes" by sequences of photodisintegrations and beta decays in explosive conditions in both core collapse supernovae (SNe II) and in Type Ia supernovae (SNe Ia). SNe II contribute to the production of p-nuclei through explosive neon and oxygen burning. However, the major problem in SN II ejecta is a general underproduction of the light p-nuclei for A < 120. We explore SNe Ia as p-process sites in the framework of a two-dimensional SN Ia delayed detonation model as well as pure deflagration models. The white dwarf precursor is assumed to have reached the Chandrasekhar mass in a binary system by mass accretion from a giant/main-sequence companion. We use enhanced s-seed distributions, with seeds directly obtained from a sequence of thermal pulse instabilities both in the asymptotic giant branch phase and in the accreted material. We apply the tracer-particle method to reconstruct the nucleosynthesis by the thermal histories of Lagrangian particles, passively advected in the hydrodynamic calculations. For each particle, we follow the explosive nucleosynthesis with a detailed nuclear reaction network for all isotopes up to 209Bi. We select tracers within the typical temperature range for p-process production, (1.5-3.7) × 109K, and analyze in detail their behavior, exploring the influence of different s-process distributions on the p-process nucleosynthesis. In addition, we discuss the sensitivity of p-process production to parameters of the explosion mechanism, taking into account the consequences on Fe and alpha elements. We find that SNe Ia can produce a large amount of p-nuclei, both the light p-nuclei below A = 120 and the heavy-p nuclei, at quite flat average production factors, tightly related to the s-process seed distribution. For the first time, we find a stellar source able to produce both light and heavy p-nuclei almost at the same level as 56Fe, including the debated neutron magic 92, 94Mo and 96, 98Ru. We also find that there is an important contribution from the p-process nucleosynthesis to the s-only nuclei 80Kr, 86Sr, to the neutron magic 90Zr, and to the neutron-rich 96Zr. Finally, we investigate the metallicity effect on p-process production in our models. Starting with different s-process seed distributions for two metallicities Z = 0.02 and Z = 0.001, running two-dimensional SN Ia models with different initial composition, we estimate that SNe Ia can contribute to at least 50% of the solar p-process composition. A more detailed analysis of the role of SNe Ia in Galactic chemical evolution of p-nuclei is in preparation. © 2011 The American Astronomical Society. All rights reserved.


Mignone A.,University of Turin | Tzeferacos P.,University of Turin | Bodo G.,National institute for astrophysics
Journal of Computational Physics | Year: 2010

We present and compare third- as well as fifth-order accurate finite difference schemes for the numerical solution of the compressible ideal MHD equations in multiple spatial dimensions. The selected methods lean on four different reconstruction techniques based on recently improved versions of the weighted essentially non-oscillatory (WENO) schemes, monotonicity preserving (MP) schemes as well as slope-limited polynomial reconstruction. The proposed numerical methods are highly accurate in smooth regions of the flow, avoid loss of accuracy in proximity of smooth extrema and provide sharp non-oscillatory transitions at discontinuities.We suggest a numerical formulation based on a cell-centered approach where all of the primary flow variables are discretized at the zone center. The divergence-free condition is enforced by augmenting the MHD equations with a generalized Lagrange multiplier yielding a mixed hyperbolic/parabolic correction, as in Dedner et al. [J. Comput. Phys. 175 (2002) 645-673]. The resulting family of schemes is robust, cost-effective and straightforward to implement. Compared to previous existing approaches, it completely avoids the CPU intensive workload associated with an elliptic divergence cleaning step and the additional complexities required by staggered mesh algorithms.Extensive numerical testing demonstrate the robustness and reliability of the proposed framework for computations involving both smooth and discontinuous features. © 2010 Elsevier Inc.


Valenti E.,European Southern Observatory | Valenti E.,University of Chile | Ferraro F.R.,University of Bologna | Origlia L.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present near-infrared colour-magnitude diagrams and physical parameters for a sample of 12 galactic globular clusters located towards the inner bulge region. For each cluster we provide measurements of the reddening, distance and photometric metallicity and of the luminosity of the horizontal branch red clump and the red giant branch bump and tip. The sample discussed here, together with that presented in Valenti, Ferraro & Origlia (2007), represents the largest homogeneous catalogue of bulge globular clusters (comprising ∼80 per cent of the entire bulge cluster population) ever studied.The compilation is available in electronic form on the World Wide Web (http://www.bo.astro.it/~GC/ir_archive). © 2009 The Authors. Journal compilation © 2009 RAS.


Rubele S.,National institute for astrophysics | Rubele S.,University of Padua | Kerber L.,University Estadual Of Santa Cruz | Girardi L.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

The rich Small Magellanic Cloud (SMC) star cluster NGC 419 has recently been found to present both a broad main-sequence turn-off and a dual red clump of giants in the sharp colour-magnitude diagrams (CMDs) derived from the High-Resolution Channel of the Advanced Camera for Surveys onboard the Hubble Space Telescope. In this work, we apply to the NGC 419 data the classical method of star-formation-history (SFH) recovery through CMD reconstruction, deriving for the first time this function for a star cluster with multiple turn-offs. The values for the cluster metallicity, reddening, distance and binary fraction were varied within the limits allowed by present observations. The global best-fitting solution is an excellent fit to the data, reproducing all the CMD features with striking accuracy. The corresponding star-formation rate is provided together with estimates of its random and systematic errors. Star formation is found to last for at least 700 Myr, and to have a marked peak in the middle of this interval, for an age of 1.5 Gyr. Our findings argue in favour of multiple star-formation episodes (or continuous star formation) being at the origin of the multiple main-sequence turn-offs in Magellanic Cloud clusters with ages of about 1 Gyr. It remains to be tested whether alternative hypotheses, such as a main-sequence spread caused by rotation, could produce similarly good fits to the data. © 2010 The Authors. Journal compilation © 2010 RAS.


Bodo G.,National institute for astrophysics | Cattaneo F.,University of Chicago | Mignone A.,University of Turin | Rossi P.,National institute for astrophysics
Astrophysical Journal | Year: 2012

We present a numerical study of turbulence and dynamo action in stratified shearing boxes with zero mean magnetic flux. We assume that the fluid obeys the perfect gas law and has finite (constant) thermal diffusivity. The calculations begin from an isothermal state spanning three scale heights above and below the mid-plane. After a long transient the layers settle to a stationary state in which thermal losses out of the boundaries are balanced by dissipative heating. We identify two regimes. The first is a conductive regime in which the heat is transported mostly by conduction and the density decreases with height. In the limit of large thermal diffusivity this regime resembles the more familiar isothermal case. The second is the convective regime, observed at smaller values of the thermal diffusivity, in which the layer becomes unstable to overturning motions, the heat is carried mostly by advection, and the density becomes nearly constant throughout the layer. In this latter constant-density regime we observe evidence for large-scale dynamo action leading to a substantial increase in transport efficiency relative to the conductive case. © 2012. The American Astronomical Society. All rights reserved..


Martin A.M.,NASA | Martin A.M.,Cornell University | Giovanelli R.,Cornell University | Haynes M.P.,Cornell University | Guzzo L.,National institute for astrophysics
Astrophysical Journal | Year: 2012

The 40% Arecibo Legacy Fast ALFA survey catalog (α.40) of 10,150 H I-selected galaxies is used to analyze the clustering properties of gas-rich galaxies. By employing the Landy-Szalay estimator and a full covariance analysis for the two-point galaxy-galaxy correlation function, we obtain the real-space correlation function and model it as a power law, ξ(r) = (r/r 0)-γ, on scales <10 h -1Mpc. As the largest sample of blindly H I-selected galaxies to date, α.40 provides detailed understanding of the clustering of this population. We find γ = 1.51 ± 0.09 and r0 = 3.3 + 0.3, -0.2 h -1Mpc, reinforcing the understanding that gas-rich galaxies represent the most weakly clustered galaxy population known; we also observe a departure from a pure power-law shape at intermediate scales, as predicted in ΛCDM halo occupation distribution models. Furthermore, we measure the bias parameter for the α.40 galaxy sample and find that H I galaxies are severely antibiased on small scales, but only weakly antibiased on large scales. The robust measurement of the correlation function for gas-rich galaxies obtained via the α.40 sample constrains models of the distribution of H I in simulated galaxies, and will be employed to better understand the role of gas in environmentally dependent galaxy evolution. © 2012 The American Astronomical Society. All rights reserved.


Milisavljevic D.,Dartmouth College | Milisavljevic D.,Harvard - Smithsonian Center for Astrophysics | Fesen R.A.,Dartmouth College | Chevalier R.A.,University of Virginia | And 3 more authors.
Astrophysical Journal | Year: 2012

Ground-based optical spectra and Hubble Space Telescope images of 10 core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and the progenitor star's circumstellar material. The most distinct trend is an increase in the strength of [O III]/([O I]+[O II]) with age, and a decline in Hα/([O I]+[O II]) which is broadly consistent with the view that the reverse shock has passed through the H envelope of the ejecta in many of these objects. We also present a spatially integrated spectrum of the young Galactic supernova remnant Cassiopeia A (Cas A). Similarities observed between the emission line profiles of the 330yr old Cas A remnant and decades old CCSNe suggest that observed emission line asymmetry in evolved CCSN spectra may be associated with dust in the ejecta, and that minor peak substructure typically interpreted as "clumps" or "blobs" of ejecta may instead be linked with large-scale rings of SN debris. © 2012. The American Astronomical Society. All rights reserved..


Baldi R.D.,University of Turin | Baldi R.D.,National institute for astrophysics | Capetti A.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2010

In a previous paper we showed that the radio sources selected by combining large area radio and optical surveys, have a strong deficit of radio emission with respect to 3CR radio-galaxies matched in line emission luminosity. We argued that the prevalence of sources with luminous extended radio structures in high flux-limited samples is due to a selection bias. Sources with low radio power form the bulk of the radio-loud AGN population but are still virtually unexplored. We here analyze their photometric and spectroscopic properties. From the point of view of their emission lines, the majority of the sample are Low Excitation Galaxies (LEG), similar to the 3CR objects at the same level of line luminosity. The hosts of the LEG are red, massive (10.5 ≲ log M*/M⊙ ≲ 12) Early-Type Galaxies (ETG) with large black hole masses (7.7 ≲ log MBH/M⊙ ≲ 9), statistically indistinguishable from the hosts of low redshift 3CR/LEG sources. No genuine radio-loud LEG could be found associated with black holes with a mass substantially smaller than 108 M⊙ or with a late type host. The fraction of galaxies with signs of star formation (∼ 5%) is similar to what is found in both the quiescent ETG and 3CR/LEG hosts. We conclude that the deficit in radio emission cannot be ascribed to differences in the properties of their hosts. We argue that instead this could be due to a temporal evolution of the radio luminosity. A minority (∼10%) of the sample show rather different properties; these are associated with low black hole masses, with spiral galaxies, or with a high excitation spectrum. In general these outliers are the result of the contamination from Seyfert galaxies and from those where the radio emission is powered by star formation. For the objects with high excitation spectra there is no clear discontinuity in either the host or nuclear properties because they include radio-quiet as well as radio-loud AGN. © 2010 ESO.


Schneider R.,National institute for astrophysics | Omukai K.,Japan National Astronomical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2010

We investigate the effects of the cosmic microwave background (CMB) radiation field on the collapse of pre-stellar clouds. Using a semi-analytic model to follow the thermal evolution of clouds with varying initial metallicities and dust contents at different redshifts, we study self-consistently the response of the mean Jeans mass at cloud fragmentation to metal line cooling, dust cooling and the CMB.In the absence of dust grains, at redshifts z ≤ 10 moderate characteristic masses (of tens of M. ⊙) are formed when the metallicity is 10-4 Z⊙ ≤ Z ≤ 10-2.5 Z⊙; at higher metallicities, the CMB inhibits fragmentation and only very large masses (of approximately hundreds of M. ⊙) are formed. These effects become even more dramatic at z > 10 and the fragmentation mass scales are always ≥hundreds of M. ⊙, independent of the initial metallicity.When dust grains are present, sub-solar mass fragments are formed at any redshift for metallicities Z ≥ 10-6 Z⊙ because dust cooling remains relatively insensitive to the presence of the CMB. When Z > 10-3 Z⊙, heating of dust grains by the CMB at z ≥ 5 favours the formation of larger masses, which become super-solar when Z ≥ 10-2 Z⊙ and z ≥ 10. Finally, we discuss the implications of our result for the interpretation of the observed abundance patterns of very metal-poor stars in the Galactic halo. © 2009 The Authors. Journal compilation © 2009 RAS.


Mignone A.,University of Turin | Rossi P.,National institute for astrophysics | Bodo G.,National institute for astrophysics | Ferrari A.,University of Turin | Massaglia S.,University of Turin
Monthly Notices of the Royal Astronomical Society | Year: 2010

Relativistic magnetized jets are key elements in active galactic nuclei and in other astrophysical environments. Their structure and evolution involve a complex non-linear physics that can be approached by numerical studies only. Still, owing to a number of challenging computational aspects, only a few numerical investigations have been undertaken so far. In this paper, we present high-resolution three-dimensional numerical simulations of relativistic magnetized jets carrying an initially toroidal magnetic field. The presence of a substantial toroidal component of the field is nowadays commonly invoked and held responsible for the process of jet acceleration and collimation. We find that the typical nose cone structures, commonly observed in axisymmetric two-dimensional simulations, are not produced in the three-dimensional case. Rather, the toroidal field gives rise to strong current-driven kink instabilities leading to jet wiggling. However, it appears to be able to maintain a highly relativistic spine along its full length. By comparing low- and high-resolution simulations, we emphasize the impact of resolution on the jet dynamical properties. © 2010 The Authors. Journal compilation © 2010 RAS.


Stanghellini L.,National Optical Astronomy Observatory | Magrini L.,National institute for astrophysics | Casasola V.,National institute for astrophysics
Astrophysical Journal | Year: 2015

Gas-phase abundances in H ii regions of two spiral galaxies, NGC 7793 and NGC 4945, have been studied to determine their radial metallicity gradients. We used the strong-line method to derive oxygen abundances from spectra acquired with GMOS-S, the multi-object spectrograph on the 8 m Gemini South telescope. We found that NGC 7793 has a well-defined gas-phase radial oxygen gradient of -0.321 ± 0.112 dex (or -0.054 ± 0.019 dex kpc-1) in the galactocentric range 0.17 < RG/R25 < 0.82, not dissimilar from gradients calculated with direct abundance methods in galaxies of similar mass and morphology. We also determined a shallow radial oxygen gradient in NGC 4945, -0.253 ± 0.149 dex (or -0.019 ± 0.011 dex kpc-1) for 0.04 < RG/R25 < 0.51, where the larger relative uncertainty derives mostly from the larger inclination of this galaxy. NGC 7793 and NGC 4945 have been selected for this study because they are similar, in mass and morphology, to M33 and the Milky Way, respectively. Since at zeroth order we expect the radial metallicity gradients to depend on mass and galaxy type, we compared our galaxies in the framework of radial metallicity models best suited for M33 and the Galaxy. We found a good agreement between M33 and NGC 7793, pointing toward similar evolution for the two galaxies. We notice instead differences between NGC 4945 and the radial metallicity gradient model that best fits the Milky Way. We found that these differences are likely related to the presence of an active galactic nucleus combined with a bar in the central regions of NGC 4945, and to its interacting environment. © 2015. The American Astronomical Society. All rights reserved..


Geller M.J.,Smithsonian Astrophysical Observatory | Kurtz M.J.,Smithsonian Astrophysical Observatory | Dell'Antonio I.P.,Brown University | Ramella M.,National institute for astrophysics | Fabricant D.G.,Smithsonian Astrophysical Observatory
Astrophysical Journal | Year: 2010

Weak-lensing surveys are emerging as an important tool for the construction of "mass-selected" clusters of galaxies. We evaluate both the efficiency and completeness of a weak-lensing selection by combining a dense, complete redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), with a weak-lensing map from the Deep Lens Survey (DLS). SHELS includes 11,692 redshifts for galaxies with R ≤ 20.6 in the 4deg2 DLS field; the survey is a solid basis for identifying massive clusters of galaxies with redshift z ≲ 0.55. The range of sensitivity of the redshift survey is similar to the range for the DLS convergence map. Only four of the 12 convergence peaks with signal to noise ≥3.5 correspond to clusters of galaxies with M ≳ 1.7 × 1014 M ⊙. Four of the eight massive clusters in SHELS are detected in the weak-lensing map yielding a completeness of 50%. We examine the seven known extended cluster X-ray sources in the DLS field: three can be detected in the weak-lensing map, three should not be detected without boosting from superposed large-scale structure, and one is mysteriously undetected even though its optical properties suggest that it should produce a detectable lensing signal. Taken together, these results underscore the need for more extensive comparisons among different methods of massive cluster identification. © 2010 The American Astronomical Society.


Rich R.M.,University of California at Los Angeles | Origlia L.,National institute for astrophysics | Valenti E.,European Southern Observatory
Astrophysical Journal | Year: 2012

We report abundance analysis for 30M giant stars in two inner Galactic bulge fields at (l, b) = (0°, -175) and at (l, b) = (1°, -265), based on R = 25,000 infrared spectroscopy (1.5-1.8 μm) using NIRSPEC at the Keck II telescope. We find iron abundances of 〈[Fe/H]〉 = -0.16 0.03dex with a 1σ dispersion of 0.12 0.02 and 〈[Fe/H]〉 = -0.21 0.02dex, with a 1σ dispersion of 0.09 0.016 for the (l, b) = (0°, -175) and (l, b) = (1°, -265) fields, respectively. In agreement with all prior studies, we find enhanced [α/Fe] of +0.3dex. We confirm the lack of any major vertical abundance or composition gradient in the innermost 600pc between Baade's Window, at (l, b) = (1°, -39), and 150pc from the Galactic plane. We also confirm that the known enhancement of alpha elements observed between 500 and 1000pc from the nucleus is also present over the volume of the inner bulge and may therefore be presumed to be characteristic of all bulge/bar stars within 1kpc of the Galactic center. © 2012. The American Astronomical Society. All rights reserved.


Zibetti S.,National institute for astrophysics | Zibetti S.,Copenhagen University | Gallazzi A.,Copenhagen University | Charlot S.,University Pierre and Marie Curie | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present Very Large Telescope Infrared Spectrometer And Array Camera (ISAAC) nearinfrared (NIR) spectrophotometric observations of 16 post-starburst galaxies aimed at constraining the debated influence of thermally pulsing asymptotic giant branch (TP-AGB) stars on the spectral energy distribution (SED) of galaxies with stellar ages between 0.5 and 2 Gyr, hence critical for high-redshift studies. Post-starburst galaxies are characterized by negligible ongoing star formation and a SED dominated by the stellar population formed in a recent (<2 Gyr) burst. By selecting post-starburst galaxies with mean luminosity-weighted ages between 0.5 and 1.5 Gyr and a broad range of metallicities (based on Sloan Digital Sky Survey optical spectroscopy), we explore the parameter space over which the relative energy output of TP-AGB stars peaks. A key feature of the present study is that we target galaxies at z ≈ 0.2, so that two main spectral features of TP-AGB stars (C-molecule band-head drops at 1.41 and 1.77 μm, blended with strong telluric absorption features, hence hardly observable from the ground, for targets at z ≈ 0) move inside the H and K atmospheric windows and can be constrained for the first time to high accuracy. Our observations provide key constraints to stellar population synthesis models. Our main results are (i) the NIR regions around 1.41 and 1.77 μm (rest frame) are featureless for all galaxies in our sample over the whole range of relevant ages and metallicities at variance with the Maraston 'TP-AGB heavy' models, which exhibit marked drops there, and (ii) no flux boosting is observed in the NIR. The optical-NIR SEDs of most of our post-starburst galaxies can be consistently reproduced with the 2003 version of the Bruzual & Charlot models, using either simple stellar populations of corresponding light-weighted ages and metallicities or a more realistic burst plus an underlying old population containing up to approximately 60 per cent of the total stellar mass. In contrast, all combinations of this kind based on the Maraston models are unable to simultaneously reproduce the smoothness of the NIR spectra and the relatively blue optical-NIR colours in the observations. The data collected in this study appear to disfavour 'TP-AGB heavy' models with respect to 'TP-AGB light' ones. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Renzini A.,National institute for astrophysics | Renzini A.,Japan National Astronomical Observatory
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2016

The evolution with cosmic time of the star formation rate density (SFRD) and of the mainsequence star formation rate-stellar mass relations are two well-established observational facts. In this Letter, the implications of these two relations combined are analytically explored, showing that quenching of star formation must start already at very early cosmic times and the quenched fraction then dominates ever since over the star-forming one. Thus, a simple picture of the cosmic evolution of the global SFRD is derived, in terms of the interplay between star formation and its quenching. © 2016 The Author.


Murante G.,Osservatorio di Turin | Poglio E.,University of Turin | Curir A.,Osservatorio di Turin | Villalobos A.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2010

We provide a set of numerical N-body simulations for studying the formation of the outer Milky Ways' stellar halo through accretion events. After simulating minor mergers of prograde and retrograde orbiting satellite halos with a dark matter main halo, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions where a retrograde signal in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the Milky Way stellar halo. Our results show that, for satellites more massive than ∼ 1/40 of the main halo, the dynamical friction has a fundamental role in assembling the final velocity distributions resulting from different orbits and that retrograde satellites moving on low-inclination orbits deposit more stars in the outer halo regions and therefore can produce the counter-rotating behavior observed in the outer Milky Way halo. © 2010. The American Astronomical Society. All rights reserved.


Valenti E.,European Southern Observatory | Origlia L.,National institute for astrophysics | Rich R.M.,University of California at Los Angeles
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present the first abundance analysis based on high-resolution infrared (IR) echelle spectra of NGC 6569 and 6624, two moderately reddened globular clusters located in the outer bulge of the Galaxy. We find [Fe/H]=-0.79 ± 0.02 and -0.69 ± 0.02 dex for NGC 6569 and 6624, respectively, and an average α-element enhancement of ≈+0.43 ± 0.02 and +0.39 ± 0.02 dex, consistent with previous measurements on other metal-rich bulge clusters. We measure accurate radial velocities of 〈vr〉=-47 ± 4 and +51 ± 3kms-1 and velocity dispersions of ≈8 and 6kms-1 for NGC 6569 and 6624, respectively. Finally, we find very low 12C/13C isotopic ratio (≤7 in NGC 6624 and ≈5 in NGC 6569), confirming the presence of extramixing mechanisms during the red giant branch evolution phase. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Bodo G.,National institute for astrophysics | Cattaneo F.,University of Chicago | Ferrari A.,University of Turin | Mignone A.,University of Turin | Rossi P.,National institute for astrophysics
Astrophysical Journal | Year: 2011

We consider the problem of convergence in homogeneous shearing-box simulations of magneto-rotationally driven turbulence. When there is no mean magnetic flux, if the equations are non-dimensionalized with respect to the diffusive scale, the only free parameter in the problem is the size of the computational domain. The problem of convergence then relates to the asymptotic form of the solutions as the computational box size becomes large. By using a numerical code with a high order of accuracy we show that the solutions become asymptotically independent of domain size. We also show that cases with weak magnetic flux join smoothly to the zero-flux cases as the flux vanishes. These results are consistent with the operation of a subcritical small-scale dynamo driving the turbulence. We conclude that for this type of turbulence the angular momentum transport is proportional to the diffusive flux and therefore has limited relevance in astrophysical situations. © 2011 The American Astronomical Society. All rights reserved.


Quartin M.,University of Heidelberg | Amendola L.,University of Heidelberg | Amendola L.,National institute for astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

Two recently proposed techniques, involving the measurement of the cosmic parallax and redshift drift, provide novel ways of directly probing (over a time span of several years) the background metric of the universe and therefore shed light on the dark-energy conundrum. The former makes use of upcoming high-precision astrometry measurements to either observe or put tight constraints on cosmological anisotropy for off-center observers, while the latter employs high-precision spectroscopy to give an independent test of the present acceleration of the universe. In this paper, we show that both methods can break the degeneracy between Lemaître-Tolman-Bondi void models and more traditional dark-energy theories. Using the near-future observational missions Gaia and CODEX we show that this distinction might be made with high confidence levels in the course of a decade. © 2010 The American Physical Society.


Amendola L.,University of Heidelberg | Amendola L.,National institute for astrophysics | Kainulainen K.,University of Jyväskylä | Kainulainen K.,Helsinki Institute of Physics | And 4 more authors.
Physical Review Letters | Year: 2010

We reanalyze the supernova data from the Union Compilation including the weak-lensing effects caused by inhomogeneities. We compute the lensing probability distribution function for each background solution described by the parameters ΩM, ΩΛ, and w in the presence of inhomogeneities, approximately modeled with a single-mass population of halos. We then perform a likelihood analysis in the parameter space of Friedmann-Lemaître- Robertson-Walkera models and compare our results with the standard approach. We find that the inclusion of lensing can move the best-fit model significantly towards the cosmic concordance of the flat Lambda-Cold Dark Matter model, improving the agreement with the constraints coming from the cosmic microwave background and baryon acoustic oscillations. © 2010 The American Physical Society.


Reines A.E.,National Optical Astronomy Observatory | Comastri A.,National institute for astrophysics
Publications of the Astronomical Society of Australia | Year: 2016

Observational constraints on the birth and early evolution of massive black holes come from two extreme regimes. At high redshift, quasars signal the rapid growth of billion-solar-mass black holes and indicate that these objects began remarkably heavy and/or accreted mass at rates above the Eddington limit. At low redshift, the smallest nuclear black holes known are found in dwarf galaxies and provide the most concrete limits on the mass of black hole seeds. Here, we review current observational work in these fields that together are critical for our understanding of the origin of massive black holes in the Universe. Copyright © Astronomical Society of Australia 2016


Giannaros T.M.,Aristotle University of Thessaloniki | Melas D.,Aristotle University of Thessaloniki | Daglis I.A.,National institute for astrophysics | Keramitsoglou I.,National institute for astrophysics | Kourtidis K.,Democritus University of Thrace
Atmospheric Environment | Year: 2013

In this study, the Weather Research and Forecasting (WRF) model coupled with the Noah land surface model was tested over the city of Athens, Greece, during two selected days. Model results were compared against observations, revealing a satisfactory performance of the modeling system. According to the numerical simulation, the city of Athens exhibits higher air temperatures than its surroundings during the night (>4 °C), whereas the temperature contrast is less evident in early morning and mid-day hours. The minimum and maximum intensity of the canopy-layer heat island were found to occur in early morning and during the night, respectively. The simulations, in agreement with concurrent observations, showed that the intensity of the canopy-layer heat island has a typical diurnal cycle, characterized by high nighttime values, an abrupt decrease following sunrise, and an increase following sunset. The examination of the spatial patterns of the land surface temperature revealed the existence of a surface urban heat sink during the day. In the nighttime, the city surface temperature was found to be higher than its surroundings. Finally, a simple data assimilation algorithm for satellite-retrieved land surface temperature was evaluated. The ingestion of the land surface temperature data into the model resulted to a small reduction in the temperature bias, generally less than 0.2 °C, which was only evident during the first 4-5 h following the assimilation. © 2013 Elsevier Ltd.


Del Popolo A.,University of Catania | Del Popolo A.,University of Sao Paulo | Del Popolo A.,Kyiv National University | Del Popolo A.,Ukrainian Academy of Sciences | Cardone V.F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2012

According to the now strongly supported concordance Λ cold dark matter model, galaxies may be grossly described as a luminous component embedded in a dark matter halo. The density profile of these mass-dominating haloes may be determined by N-body simulations which mimic the evolution of the tiny initial density perturbations during the process leading to the structures we observe today. Unfortunately, when the effect of baryons is taken into account, the situation gets much more complicated due to the difficulties in simulating their physics. As a consequence, a definitive prediction of how dark matter haloes should presently look is still missing. We revisit here this issue from an observational point of view devoting our attention to dwarf galaxies. Being likely dark matter dominated, these systems are ideal candidates to investigate the present-day halo density profiles and check whether dark matter related quantities correlate with stellar ones or the environment. By fitting a large sample of well-measured rotation curves, we infer constraints on both halo structural parameters (such as the logarithmic slope of the density profile and its concentration) and derived quantities (e.g. the mass fraction and the Newtonian acceleration) which could then be used to constrain galaxy formation scenarios. Moreover, we investigate whether the halo properties correlate with the environment the galaxy lives in, thus offering a new tool to deepen our understanding of galaxy formation. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Basilakos S.,Academy of Athens | Plionis M.,National institute for astrophysics | Plionis M.,National Institute of Astrophysics, Optics and Electronics | Lima J.A.S.,University of Sao Paulo
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

The mass function of cluster-size halos and their redshift distribution are computed for 12 distinct accelerating cosmological scenarios and confronted to the predictions of the conventional flat ΛCDM model. The comparison with ΛCDM is performed by a two-step process. First, we determine the free parameters of all models through a joint analysis involving the latest cosmological data, using supernovae type Ia, the cosmic microwave background shift parameter, and baryon acoustic oscillations. Apart from a braneworld inspired cosmology, it is found that the derived Hubble relation of the remaining models reproduces the ΛCDM results approximately with the same degree of statistical confidence. Second, in order to attempt to distinguish the different dark energy models from the expectations of ΛCDM, we analyze the predicted cluster-size halo redshift distribution on the basis of two future cluster surveys: (i) an X-ray survey based on the eROSITA satellite, and (ii) a Sunayev-Zeldovich survey based on the South Pole Telescope. As a result, we find that the predictions of 8 out of 12 dark energy models can be clearly distinguished from the ΛCDM cosmology, while the predictions of 4 models are statistically equivalent to those of the ΛCDM model, as far as the expected cluster mass function and redshift distribution are concerned. The present analysis suggests that such a technique appears to be very competitive to independent tests probing the late time evolution of the Universe and the associated dark energy effects. © 2010 The American Physical Society.


Silva-Valio A.,University of Sao Paulo | Lanza A.F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2011

Context.CoRoT-2, the second planet-hosting star discovered by the CoRoT satellite, is a young and active star. A total of 77 transits were observed for this system over a period of 135 days. Aims.Small modulations detected in the optical light curve of the planetary transits are used to study the position, size, intensity, and temporal evolution of the photospheric spots on the surface of the star that are occulted by the planetary disk. Methods.We apply a spot model to these variations and create a spot map of the stellar surface of CoRoT-2 within the transit band for every transit. From these maps, we estimate the stellar rotation period and obtain the longitudes of the spots in a reference frame rotating with the star. Moreover, the spots temporal evolution is determined. This model achieves a spatial resolution of 2°. Results.Mapping of 392 spots vs. longitude indicates the presence of a region free of spots, close to the equator, which is reminiscent of the coronal holes observed on the Sun during periods of maximum activity. With this interpretation, the stellar rotation period within the transit latitudes of â̂'14.°6±10° is obtained from the auto-correlation function of the time-integrated spot flux deficit, which yields a rotation period of 4.48 days. With this period, the temporal evolution of the spot surface coverage in individual 20° longitude bins has periodicities ranging from 9 to 53 days with an average value of 31 ± 15 days. On the other hand, the longitude integrated spot flux, which is independent of the stellar rotation period, oscillates with a periodicity of 17.7 days, and its false-alarm probability is ∼ 3%. Conclusions.The rotation period of 4.48 days obtained here is shorter than the 4.54 days derived from the out-of-transit light modulation. Because the transit data sample a region close to the stellar equator while the period determined from out-of-transit data reflects the average rotation of the star, this is taken as an indication of a latitudinal differential rotation of about 3% or 0.042 rad/d. © 2011 ESO.


Rubele S.,National institute for astrophysics | Rubele S.,University of Padua | Girardi L.,National institute for astrophysics | Kozhurina-Platais V.,US Space Telescope Science Institute | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

The HST/ACS colour-magnitude diagrams (CMDs) of the populous Large Magellanic Cloud (LMC) star cluster NGC 1751 present both a broad main-sequence turn-off and a dual clump of red giants. We show that the latter feature is real and associate it to the first appearance of electron degeneracy in the H-exhausted cores of the cluster stars. We then apply to the NGC 1751 data the classical method of star formation history (SFH) recovery via CMD reconstruction, for different radii corresponding to the cluster centre, the cluster outskirts and the underlying LMC field. The mean SFH derived from the LMC field is taken into account during the stage of SFH recovery in the cluster regions, in a novel approach which is shown to significantly improve the quality of the SFH results. For the cluster centre, we find a best-fitting solution corresponding to prolonged star formation for a time-span of 460Myr, instead of the two peaks separated by 200Myr favoured by a previous work based on isochrone fitting. Remarkably, our global best-fitting solution provides an excellent fit to the data - with χ2 and residuals close to the theoretical minimum - reproducing all the CMD features including the dual red clump. The results for a larger ring region around the centre indicate even longer star formation, but in this case the results are of lower quality, probably because of the differential extinction detected in the area. Therefore, the presence of age gradients in NGC 1751 could not be probed. Together with our previous findings for the Small Magellanic Cloud (SMC) cluster NGC 419, the present results for the NGC 1751 centre argue in favour of multiple star formation episodes (or continued star formation) being at the origin of the multiple main-sequence turn-offs in Magellanic Cloud clusters with ages around 1.5 Gyr. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Koutoulidis L.,National Observatory of Athens | Koutoulidis L.,University of Patras | Plionis M.,Aristotle University of Thessaloniki | Plionis M.,National Institute of Astrophysics, Optics and Electronics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present the spatial clustering properties of 1466 X-ray-selected active galactic nuclei (AGN) compiled from the Chandra Deep Field (CDF) North and South, extended CDF-S, COSMOS and All-wavelength Extended Groth strip International Survey (AEGIS) fields in the 0.5-8 keV band. The X-ray sources span the redshift interval 0 < z < 3 and have a median value of z = 0.976. We employ the projected two-point correlation function to infer the spatial clustering and find a clustering length of r0 = 7.2 ± 0.6 h-1 Mpc and a slope of γ = 1.48 ± 0.12, which corresponds to a bias of b(z) = 2.26 ± 0.16. Using two different halo bias models, we consistently estimate an average dark-matter host halo mass of Mh ~ 1.3(± 0.3) × 1013 h-1M~. The X-ray AGN bias and the corresponding dark-matter host halo mass are significantly higher than the corresponding values of optically selected AGN (at the same redshifts). The redshift evolution of the X-ray-selected AGN bias indicates, in agreement with other recent studies, that a unique dark-matter halo mass does not fit well the bias at all the different redshifts probed. Furthermore, we investigate if there is a dependence of the clustering strength on X-ray luminosity. To this end we consider only 650 sources around z ~ 1 and we apply a procedure to disentangle the dependence of clustering on redshift. We find indications for a positive dependence of the clustering length on X-ray luminosity, in the sense that the more luminous sources have a larger clustering length and hence a higher dark-matter halo mass. In detail we find for an average luminosity difference of δ log10Lx ~ 1 a halo mass difference of a factor of ~3. These findings appear to be consistent with a galaxy formation model where the gas accreted on to the supermassive black hole in intermediate-luminosity AGN comes mostly from the hot-halo atmosphere around the host galaxy. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Origlia L.,National institute for astrophysics | Massari D.,University of Bologna | Rich R.M.,University of California at Los Angeles | Mucciarelli A.,University of Bologna | And 3 more authors.
Astrophysical Journal Letters | Year: 2013

We report on the discovery of three metal-poor giant stars in Terzan 5, a complex stellar system in the Galactic bulge, known to have two populations at [Fe/H] = -0.25 and +0.3. For these three stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide an average [Fe/H] = -0.79 dex iron abundance and [α/Fe] = +0.36 dex enhancement. This new population extends the metallicity range of Terzan 5 to 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core-collapse supernovae. © 2013. The American Astronomical Society. All rights reserved.


Rubele S.,National institute for astrophysics | Girardi L.,National institute for astrophysics | Kozhurina-Platais V.,US Space Telescope Science Institute | Kerber L.,University Estadual Of Santa Cruz | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

NGC 1846 and NGC 1783 are two massive star clusters in the Large Magellanic Cloud, hosting both an extended main-sequence turn-off and a dual clump of red giants. They present similar masses but differ mainly in angular size. Starting from their high-quality ACS data in the F435W, F555W and F814W filters, and updated sets of stellar evolutionary tracks, we derive their star formation rates as a function of age, SFR(t), by means of the classical method of colour-magnitude diagram reconstruction which is usually applied to nearby galaxies. The method confirms the extended periods of star formation derived from previous analysis of the same data. When the analysis is performed for a finer resolution in age, we find clear evidence for a ~50-Myr long hiatus between the oldest peak in the SFR(t), and a second prolonged period of star formation, in both clusters. For the more compact cluster NGC 1846, there seems to be no significant difference between the SFR(t) in the cluster centre and in an annulus with radii between 20 and 60 arcsec (from 4.8 to 15.4 pc). The same does not occur in the more extended NGC 1783 cluster, where the outer ring (between 33 and 107 arcsec, from 8.0 to 25.9 pc) is found to be slightly younger than the centre. We also explore the best-fitting slope of the present-day mass function and binary fraction for the different cluster regions, finding hints of a varying mass function between centre and outer ring in NGC 1783. These findings are discussed within the present scenarios for the formation of clusters with multiple turn-offs. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Serra A.L.,National institute for astrophysics | Serra A.L.,University of Turin | Serra A.L.,National Institute of Nuclear Physics, Italy | Diaferio A.,University of Turin | Diaferio A.,National Institute of Nuclear Physics, Italy
Astrophysical Journal | Year: 2013

The caustic technique measures the mass of galaxy clusters in both their virial and infall regions and, as a byproduct, yields the list of cluster galaxy members. Here we use 100 galaxy clusters with mass M·200 ≥ 1014 h -1 M· extracted from a cosmological N-body simulation of a ΛCDM universe to test the ability of the caustic technique to identify the cluster galaxy members. We identify the true three-dimensional members as the gravitationally bound galaxies. The caustic technique uses the caustic location in the redshift diagram to separate the cluster members from the interlopers. We apply the technique to mock catalogs containing 1000 galaxies in the field of view of 12 h -1 Mpc on a side at the cluster location. On average, this sample size roughly corresponds to 180 real galaxy members within 3r200, similar to recent redshift surveys of cluster regions. The caustic technique yields a completeness, the fraction of identified true members, fc = 0.95 ± 0.03, within 3r200. The contamination, the fraction of interlopers in the observed catalog of members, increases from at r 200 to at 3r200. No other technique for the identification of the members of a galaxy cluster provides such large completeness and small contamination at these large radii. The caustic technique assumes spherical symmetry and the asphericity of the cluster is responsible for most of the spread of the completeness and the contamination. By applying the technique to an approximately spherical system obtained by stacking the individual clusters, the spreads decrease by at least a factor of two. We finally estimate the cluster mass within 3r200 after removing the interlopers: for individual clusters, the mass estimated with the virial theorem is unbiased and within 30% of the actual mass; this spread decreases to less than 10% for the spherically symmetric stacked cluster. © 2013. The American Astronomical Society. All rights reserved.


Geller M.J.,Smithsonian Astrophysical Observatory | Diaferio A.,University of Turin | Rines K.J.,Western Washington University | Serra A.L.,University of Turin | And 2 more authors.
Astrophysical Journal | Year: 2013

Cluster mass profiles are tests of models of structure formation. Only two current observational methods of determining the mass profile, gravitational lensing, and the caustic technique are independent of the assumption of dynamical equilibrium. Both techniques enable the determination of the extended mass profile at radii beyond the virial radius. For 19 clusters, we compare the mass profile based on the caustic technique with weak lensing measurements taken from the literature. This comparison offers a test of systematic issues in both techniques. Around the virial radius, the two methods of mass estimation agree to within ∼30%, consistent with the expected errors in the individual techniques. At small radii, the caustic technique overestimates the mass as expected from numerical simulations. The ratio between the lensing profile and the caustic mass profile at these radii suggests that the weak lensing profiles are a good representation of the true mass profile. At radii larger than the virial radius, the extrapolated Navarro, Frenk & White fit to the lensing mass profile exceeds the caustic mass profile. Contamination of the lensing profile by unrelated structures within the lensing kernel may be an issue in some cases; we highlight the clusters MS0906+11 and A750, superposed along the line of sight, to illustrate the potential seriousness of contamination of the weak lensing signal by these unrelated structures. © 2013. The American Astronomical Society. All rights reserved.


Ortolani S.,University of Padua | Ortolani S.,National institute for astrophysics | Bica E.,Federal University of Rio Grande do Sul | Barbuy B.,University of Sao Paulo
Monthly Notices of the Royal Astronomical Society | Year: 2013

Deep Galileo (Telescopio Nazionale Galileo) B, V and I images of Segue 3, reaching V ∼ 25, reveal that it is the youngest globular cluster known so far in the Galaxy. A young age of 3.2 Gyr is found, differently from a previous estimate of 12 Gyr. It also appears to be moderately metal rich with [Fe/H] ∼ -0.8, rather than |Fe/H] ∼ -1.7, as previously suggested by Fadely et al. A main difference in the age derivation relative to Fadely et al. comes from the consideration of subgiant branch stars in the isochrone fitting. A deduced distance of d⊙ = 29.1 kpc is compatible with the outer halo location of other low luminosity globular clusters. © 2013 The Authors.


Bodo G.,National institute for astrophysics | Cattaneo F.,University of Chicago | Mignone A.,University of Turin | Rossi P.,National institute for astrophysics
Astrophysical Journal Letters | Year: 2013

We present a numerical study of turbulence and dynamo action in stratified shearing boxes with zero magnetic flux. We assume that the fluid obeys the perfect gas law and has finite (constant) thermal diffusivity. We choose radiative boundary conditions at the vertical boundaries in which the heat flux is proportional to the fourth power of the temperature. We compare the results with the corresponding cases in which fixed temperature boundary conditions are applied. The most notable result is that the formation of a fully convective state in which the density is nearly constant as a function of height and the heat is transported to the upper and lower boundaries by overturning motions is robust and persists even in cases with radiative boundary conditions. Interestingly, in the convective regime, although the diffusive transport is negligible, the mean stratification does not relax to an adiabatic state. © 2013. The American Astronomical Society. All rights reserved.


Bodo G.,National institute for astrophysics | Mamatsashvili G.,Tbilisi State University | Rossi P.,National institute for astrophysics | Mignone A.,University of Turin
Monthly Notices of the Royal Astronomical Society | Year: 2013

We perform a linear analysis of the stability of amagnetized relativistic non-rotating cylindrical flow in the approximation of zero thermal pressure, considering only the |m| = 1 mode. We find that there are two modes of instability: Kelvin-Helmholtz and current driven. The Kelvin- Helmholtz mode is found at low magnetizations and its growth rate depends very weakly on the pitch parameter. The current-driven modes are found at high magnetizations and the value of the growth rate and the wavenumber of the maximum increase as we decrease the pitch parameter. In the relativistic regime the current-drivenmode is split in two branches, the branch at high wavenumbers is characterized by the eigenfunction concentrated in the jet core; the branch at low wavenumbers is instead characterized by the eigenfunction that extends outside the jet velocity shear region. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Valiante R.,University of Florence | Valiante R.,National institute for astrophysics | Schneider R.,National institute for astrophysics | Salvadori S.,NOVA Kapteyn Astronomical Institute | Bianchi S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present a semi-analytical model for the formation and evolution of a high-redshift quasar (QSO). We reconstruct a set of hierarchical merger histories of a 1013-M⊙ dark matter halo and model the evolution of the corresponding galaxy and of its central supermassive black hole. The code gamete/QSOdust consistently follows (i) the black hole assembly via both coalescence with other black holes and gas accretion; (ii) the build-up and star formation history of the quasar host galaxy, driven by binary mergers and mass accretion; (iii) the evolution of gas, stars and metals in the interstellar medium (ISM), accounting for mass exchanges with the external medium (infall and outflow processes); (iv) the dust formation in supernova (SN) ejecta and in the stellar atmosphere of asymptotic giant branch (AGB) stars, dust destruction by interstellar shocks and grain growth in molecular clouds; and (v) the active galactic nucleus feedback which powers a galactic-scale wind, self-regulating the black hole growth and eventually halting star formation. We use this model to study the case of SDSS J1148+5251 observed at redshift 6.4. We explore different star formation histories for the QSO host galaxy and find that Population III stars give a negligible contribution to the final metal and dust masses due to rapid enrichment of the ISM to metallicities >Zcr= 10-6-10-4Z⊙ in progenitor galaxies at redshifts >10. If Population II/I stars form with a standard initial mass function (IMF) and with a characteristic stellar mass ofmch= 0.35M⊙, a final stellar mass of (1-5) × 1011M⊙ is required to reproduce the observed dust mass and gas metallicity of SDSS J1148+5251. This is a factor of 3-10 higher than the stellar mass inferred from observations and would shift the QSO closer or on to the stellar bulge-black hole relation observed in the local Universe; alternatively, the observed chemical properties can be reconciled with the inferred stellar mass, assuming that Population II/I stars form according to a top-heavy IMF withmch= 5M⊙. We find that SNe dominate the early dust enrichment and that, depending on the shape of the star formation history and on the stellar IMF, AGB stars contribute atz< 8-10. Yet, a dust mass of (2-6) × 108M⊙ estimated for SDSS J1148+5251 cannot be reproduced considering only stellar sources, and the final dust mass is dominated by grain growth in molecular clouds. This conclusion is independent of the stellar IMF and star formation history. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Montalban J.,Institute Dastrophysique Et Geophysique Of Luniversite Of Liege | Miglio A.,University of Birmingham | Noels A.,Institute Dastrophysique Et Geophysique Of Luniversite Of Liege | Dupret M.-A.,Institute Dastrophysique Et Geophysique Of Luniversite Of Liege | And 2 more authors.
Astrophysical Journal | Year: 2013

Uncertainties on central mixing in main-sequence (MS) and core He-burning (He-B) phases affect key predictions of stellar evolution such as late evolutionary phases, chemical enrichment, ages, etc. We propose a test of the extension of extra-mixing in two relevant evolutionary phases based on period spacing (ΔP) of solar-like oscillating giants. From stellar models and their corresponding adiabatic frequencies (respectively, computed with ATON and LOSC codes), we provide the first predictions of the observable ΔP for stars in the red giant branch and in the red clump (RC). We find (1) a clear correlation between ΔP and the mass of the helium core (M He); the latter in intermediate-mass stars depends on the MS overshooting, and hence it can be used to set constraints on extra-mixing during MS when coupled with chemical composition; and (2) a linear dependence of the average value of the asymptotic period spacing (〈ΔP〉a ) on the size of the convective core during the He-B phase. A first comparison with the inferred asymptotic period spacing for Kepler RC stars also suggests the need for extra-mixing during this phase, as evinced from other observational facts. © 2013. The American Astronomical Society. All rights reserved.


Gai M.,National institute for astrophysics | Busonero D.,National institute for astrophysics | Cancelliere R.,University of Turin
Publications of the Astronomical Society of the Pacific | Year: 2013

A general purpose fitting model for one-dimensional astrometric signals is developed, building on a maximum likelihood framework, and its performance is evaluated by simulation over a set of realistic image instances. The fit quality is analysed as a function of the number of terms used for signal expansion, and of astrometric error, rather than rms discrepancy with respect to the input signal. The tuning of the function basis to the statistical characteristics of the signal ensemble is discussed. The fit sensitivity to a priori knowledge of the source spectra is addressed. Some implications of the current results on calibration and data reduction aspects are discussed, in particular with respect to Gaia. © 2013. The Astronomical Society of the Pacific. All rights reserved. Printed in U.S.A.


Del Popolo A.,University of Catania | Del Popolo A.,University of Sao Paulo | Cardone V.F.,National institute for astrophysics | Belvedere G.,University of Catania
Monthly Notices of the Royal Astronomical Society | Year: 2013

In this paper, we analysed the correlation between the central surface density and the halo core radius of galaxies, and cluster of galaxies dark matter (DM) haloes, in the framework of the econdary infall model. We used Del Popolo secondary infall model taking into account ordered and random angular momentum, dynamical friction and DM adiabatic contraction to calculate the density profile of haloes, and then these profiles are used to determine the surface density of DM haloes. The main result is that r* (the halo characteristic radius) is not a universal quantity as claimed by Donato et al. and Gentile et al. On the contrary, we find a correlation with the halo mass M200 in agreement with Cardone & Tortora, Boyarsky et al. and Napolitano, Romanowsky & Tortora, but with a significantly smaller scatter, namely 0.16 ± 0.05. We also consider the baryon column density finding this latter being indeed a constant for low-mass systems, such as dwarfs, but correlating with mass with a slope of α = 0.18 ± 0.05. In the case of the surface density of D for a system composed only of DM, as in dissipationless simulations, we get α = 0.20 ± 0.05. These results leave little room for the recently claimed universality of (dark and stellar) column density. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Fontani F.,ESO | Fontani F.,Institut Universitaire de France | Cesaroni R.,National institute for astrophysics | Furuya R.S.,Japan National Astronomical Observatory
Astronomy and Astrophysics | Year: 2010

Context. Among the tracers of the earliest phases in the massive star formation process, methanol masers have gained increasing importance. The phenomenological distinction between Class I and II methanol masers is based on their spatial association with objects such as jets, cores, and ultracompact Hii regions, but is also believed to correspond to different pumping mechanisms: radiation for Class II masers, collisions for Class I masers. Aims. We surveyed a large sample of massive star-forming regions in Class I and II methanol masers. The sample consists of 296 sources, divided into two groups named high and low according to their [25-12] and [60-12] IRAS colours. Previous studies indicate that the two groups may contain similar sources in different evolutionary stages, with the high sources representing the more evolved stages. Therefore, the sample can be used to assess a sequence for the occurrence of Class I and II methanol masers during the evolution of a massive star-forming region. Methods. We observed the 6 GHz (Class II) CH3OH maser with the Effelsberg 100-m telescope, and the 44 GHz and 95 GHz (Class I) CH 3OH masers with the Nobeyama 45-m telescope. Results. We detected 55 sources in the Class II line (39 high and 16 low, 12 new detections); 27 sources in the 44 GHz Class I line (19 high and 8 low, 17 new detections); 11 sources in the 95 GHz Class I line (eight high and three low, all except one are new detections). The detection rate of Class II masers decreases with the distance of the source (as expected), whereas that of Class I masers peaks at ~5 kpc. This could be due to the Class I maser spots being spread over a region $\la$1 pc, comparable to the telescope beam diameter at a distance of ~5 kpc. We also find that the two Class I lines have similar spectral shapes at 44 GHz and 95 GHz, which confirms that they have the same origin. Conclusions. Our statistical analysis shows that the ratio between the detection rates of Class II and Class I methanol masers is basically the same in high and low sources. Therefore, both maser types seem to be equally associated with each evolutionary phase. In contrast, all maser species (including H 2O) have about three times higher detection rates in high than in low sources. This could indicate that the phenomena from which all masers originate become progressively more active with time during the earliest evolutionary phases of a high-mass star-forming region. © 2010 ESO.


Silva-Valio A.,University of Sao Paulo | Lanza A.F.,National institute for astrophysics | Alonso R.,French National Center for Scientific Research | Barge P.,French National Center for Scientific Research
Astronomy and Astrophysics | Year: 2010

Context. As a planet eclipses its parent star, a dark spot on the surface of the star may be occulted, causing a detectable variation in the light curve. Aims. We study these light curve variations during transits and infer the physical characteristics of the stellar spots. Methods. A total of 77 consecutive transit light curves of CoRoT-2 were observed with a high temporal resolution of 32 s, corresponding to an uninterrupted period of 134 days. By analyzing small intensity variations in the transit light curves, it was possible to detect and characterize spots on the surface of the star. The model used simulates planetary transits and enables the inclusion of spots on the stellar surface with different sizes, intensities (i.e., temperatures), and positions. Fitting the data with this model, it is possible to infer the physical characteristics of the spots. Because what is observed is the stellar flux blocked by the spots, there is a degeneracy between the spot intensity and area, although the spot radius defines the shape and width of the signal in the light curve. The model allows up to 9 spots to be present on the stellar surface within the transit band. Results. Before the modeling of the spots was performed, the planetary radius relative to the star radius was estimated by fitting the deepest transit to minimize the effect of spots. A slightly larger (3%) radius, 0.172 Rstar, resulted instead in the previously reported 0.1667 Rstar. The fitting of the transits yields spots, or spot groups, of sizes ranging from 0.2 to 0.7 planetary radius, Rp, with a mean of 0.46 ± 0.11 Rp (100 000 km), resulting in a stellar area covered by spots within the transit latitudes of 10-20%. The intensity varied from 0.3 to 0.8 of the disk center intensity, Ic, with a mean of 0.55 ± 0.13 Ic, which can be converted to temperature by assuming black-body emission for both the photosphere and the spots. Considering an effective temperature of 5625 K for the stellar photosphere, the mean spot temperature is 4700 ± 300 K. Conclusions. The spot model used here was able to estimate the physical characteristics of the spots on CoRoT-2, such as size and intensity. The spots on CoRoT-2 are larger and cooler than sunspots, maybe confirming the more active nature of this star with respect to the Sun. The results presented here are in agreement with those found for magnetic activity analysis from out of transit data of the same star. © ESO, 2010.


Hunt L.K.,National institute for astrophysics | Thuan T.X.,University of Virginia | Izotov Y.I.,Ukrainian Academy of Sciences | Sauvage M.,CEA Saclay Nuclear Research Center
Astrophysical Journal | Year: 2010

We present low- and high-resolution Spitzer/IRS spectra, supplemented by Infrared Array Camera and Multiband Imaging Photometer for Spitzer measurements, of 22 blue compact dwarf (BCD) galaxies. The BCD sample spans a wide range in oxygen abundance (12+log(O/H) between 7.4 and 8.3), and hardness of the interstellar radiation field (ISRF). The Infrared Spectrograph (IRS) spectra provide us with a rich set of diagnostics to probe the physics of star and dust formation in very low metallicity environments. We find that metal-poor BCDs have harder ionizing radiation than metal-rich galaxies: [OIV] emission is ≳4 times as common as [FeII] emission. They also have a more intense ISRF, as indicated by the 71 to 160μm luminosity ratio. Two-thirds of the sample (15 BCDs) show polycyclic aromatic hydrocarbon (PAH) features, although the fraction of PAH emission normalized to the total infrared (IR) luminosity is considerably smaller in metal-poor BCDs (∼0.5%) than in metal-rich star-forming galaxies (∼10%). We find several lines of evidence for a deficit of small PAH carriers at low metallicity, and attribute this to destruction by a hard, intense ISRF, only indirectly linked to metal abundance. Our IRS spectra reveal a variety of H2 rotational lines, and more than a third of the objects in our sample (eight BCDs) have ≳3σ detections in one or more of the four lowest-order transitions. The warm gas masses in the BCDs range from 103 M ⊙ to 10 8M ⊙, and can be comparable to the neutral hydrogen gas mass; relative to their total IR luminosities, some BCDs contain more H 2 than Spitzer Nearby Galaxy Survey galaxies. © 2010. The American Astronomical Society.


Battaglia G.,National institute for astrophysics | Helmi A.,NOVA Kapteyn Astronomical Institute | Breddels M.,NOVA Kapteyn Astronomical Institute
New Astronomy Reviews | Year: 2013

We review our current understanding of the internal dynamical properties of the dwarf spheroidal galaxies surrounding the Milky Way. These are the most dark matter dominated galaxies, and as such may be considered ideal laboratories to test the current concordance cosmological model, and in particular provide constraints on the nature of the dominant form of dark matter. We discuss the latest observations of the kinematics of stars in these systems, and how these may be used to derive their mass distribution. We tour through the various dynamical techniques used, with emphasis on the complementarity and limitations, and discuss what the results imply also in the context of cosmological models. Finally we provide an outlook on exciting developments in this field. © 2013 Elsevier B.V.


Fedeli C.,National institute for astrophysics | Moscardini L.,National institute for astrophysics | Moscardini L.,University of Bologna | Moscardini L.,National Institute of Nuclear Physics, Italy
Monthly Notices of the Royal Astronomical Society | Year: 2014

The scatter in the apparent magnitude of Type Ia supernovae induced by stochastic gravitational lensing is highly dependent on the non-linear growth of cosmological structure. In this paper, we show that such a dependence can potentially be employed to gain significant information about the mass clustering at small scales. While the mass clustering ultimately hinges on cosmology, here we demonstrate that, upon obtaining more precise observational measurements through future cosmological surveys, the lensing dispersion can very effectively be used to gain information on the poorly understood astrophysical aspects of structure formation, such as the clumpiness of dark matter haloes and the importance of gas physics and star formation into shaping the large-scale structure. In order to illustrate this point, we verify that even the tentative current measurements of the lensing dispersion performed on the Supernova Legacy Survey sample favour a scenario where virialized structures are somewhat less compact than predicted by N-body cosmological simulations. Moreover, we are also able to put lower limits on the slope of the concentration-mass relation. By artificially reducing the statistical observational error, we argue that with forthcoming data the stochastic lensing dispersion will allow one to importantly improve constraints on the baryonic physics at work during the assembly of cosmological structure. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


D'Antona F.,National institute for astrophysics | Ventura P.,National institute for astrophysics | Decressin T.,National institute for astrophysics | Vesperini E.,Indiana University Bloomington | D'Ercole A.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

We investigate the viability of a model in which the chemical anomalies among globular cluster stars are due to accretion of gas on to the protostellar discs of low-mass stars. This model has been suggested as a way to reduce the large initial cluster masses required by other models for the formation of multiple stellar generations. We numerically follow the evolution of the accreting stars, and we show that the structure of the seed star does not remain fully convective for the whole duration of the accretion phase. Stellar populations showing discrete abundances of helium in the core, that seem to be present in some clusters, might be formed with this mechanism only if accretion occurs before the core of the stars become radiative (within 2-3 Myr) or if a thermohaline instability is triggered, to achieve full mixing after the accretion phase ends.We also showthat the lithium abundances in accreted structures may vary by orders of magnitude in equal masses obtained by accreting different masses. In addition, the same thermohaline mixing which could provide a homogeneous helium distribution down to the stellar centre, would destroy any lithium surviving in the envelope, so that both helium homogeneity and lithium survival require that the accretion phase be limited to the first couple of million years of the cluster evolution. Such a short accretion phase strongly reduces the amount of processed matter available, and reintroduces the requirement of an extremely large initial mass for the protocluster. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Zamfir S.,University of Alabama | Sulentic J.W.,University of Alabama | Sulentic J.W.,Institute Astrofisica Of Andalucia | Marziani P.,National institute for astrophysics | Dultzin D.,National Autonomous University of Mexico
Monthly Notices of the Royal Astronomical Society | Year: 2010

We explore the properties of the Hβ emission line profile in a large, homogeneous and bright sample of N ∼ 470 low-redshift quasars extracted from Sloan Digital Sky Survey (Data Release 5). We approach the investigation from two complementary directions: composite/median spectra and a set of line diagnostic measures (asymmetry index, centroid shift and kurtosis) in individual quasars. The project is developed and presented in the framework of the so-called 4D Eigenvector 1 (4DE1) parameter space, with a focus on its optical dimensions, full width at half-maximum of broad Hβ[FWHM(Hβ)] and the relative strength of optical Fe ii[RFe ii≡ W(Fe ii4434-4684 Å)/W(Hβ)]. We reenforce the conclusion that not all quasars are alike and spectroscopically they do not distribute randomly about an average typical optical spectrum. Our results give further support to the concept of two populations A and B [narrower and broader than 4000 km s-1 FWHM(Hβ), respectively] that emerged in the context of 4DE1 space. The broad Hβ profiles in composite spectra of Population A sources are best described by a Lorentzian and in Population B by a double Gaussian model. Moreover, high- and low-accretion sources (an alternative view of the Population A/B concept) not only show significant differences in terms of black hole (BH) and Eddington ratio Lbol/LEdd, but they also show distinct properties in terms of line asymmetry, shift and shapes. We finally suggest that a potential refinement of the 4DE1 space can be provided by separating two populations of quasars at RFe ii∼ 0.50 rather than at FWHM(Hβ) = 4000 km s-1. Concomitantly, the asymmetry and centroid shift profile measures at 1/4 fractional intensity can be reasonable surrogates for the FWHM(Hβ) dimension of the current 4DE1. © 2010 The Authors. Journal compilation © 2010 RAS.


Pumo M.L.,National institute for astrophysics | Pumo M.L.,Bonino Pulejo Foundation | Zampieri L.,National institute for astrophysics
Astrophysical Journal | Year: 2011

We have developed a relativistic, radiation-hydrodynamics Lagrangian code, specifically tailored to simulate the evolution of the main observables (light curve and the evolution of photospheric velocity and temperature) in core-collapse supernova (CC-SN) events. The distinctive features of the code are an accurate treatment of radiative transfer coupled to relativistic hydrodynamics, a self-consistent treatment of the evolution of the innermost ejecta taking into account the gravitational effects of the central compact remnant, and a fully implicit Lagrangian approach to the solution of the coupled nonlinear finite difference system of equations. Our aim is to use it as a numerical tool to perform calculations of a grid of models to be compared with observations of CC-SNe. In this paper, we present some testcase simulations and a comparison with observations of SN 1987A, as well as with the results obtained with other numerical codes. We also briefly discuss the influence of the main physical parameters (ejected mass, progenitor radius, explosion energy, amount of 56Ni) on the evolution of the ejecta, and the implications of our results in connection with the possibility to "standardize" hydrogen-rich CC-SNe for using them as candles to measure cosmological distances. © 2011. The American Astronomical Society. All rights reserved.


Bonanno A.,National institute for astrophysics | Bonanno A.,National Institute of Nuclear Physics, Italy | Reuter M.,University of Mainz
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We discuss the stabilization of the conformal factor by higher derivative terms in a conformally reduced R+R2 Euclidean gravity theory. The flat spacetime is unstable towards the condensation of modes with nonzero momentum, and they "condense" in a modulated phase above a critical value of the coupling β of the R2 term. By employing a combination of variational, numerical and lattice methods, we show that in the semiclassical limit the corresponding functional integral is dominated by a single nonlinear plane wave of frequency ≈1/√βℓPl. We argue that the ground state of the theory is characterized by a spontaneous breaking of translational invariance at Planckian scales. © 2013 American Physical Society.


Ofman L.,Catholic University of America | Ofman L.,Tel Aviv University | Abbo L.,National institute for astrophysics | Giordano S.,National institute for astrophysics
Astrophysical Journal | Year: 2011

We present the results of a time-dependent 2.5-dimensional three-fluid magnetohydrodynamic model of the coronal streamer belt, which is compared with the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO during the past minimum of solar activity (Carrington Rotation 1913). Our previous three-fluid streamer model has been improved by considering the solar magnetic field configuration relevant for solar minimum conditions, and preferential heating for O5 + ions. The model was run until a fully self-consistent streamer solution was obtained in the quasi-steady state. The plasma parameters from the multi-fluid model were used to compute the expected UV observables from H I Lyα 1216 and O VI 1032 spectral lines, and the results were compared in detail with the UVCS measurements. A good agreement between the model and the data was found. The results of the study provide insight into the acceleration and heating of the multi-ion slow solar wind. © 2011. The American Astronomical Society. All rights reserved.


Bird S.,Institute of Astronomy and Kavli Institute for Cosmology | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy | Haehnelt M.G.,Institute of Astronomy and Kavli Institute for Cosmology
Monthly Notices of the Royal Astronomical Society | Year: 2012

We perform an extensive suite of N-body simulations of the matter power spectrum, incorporating massive neutrinos in the range M ν= 0.15-0.6eV, probing the non-linear regime at scales k < 10hMpc -1 at z < 3. We extend the widely used halofit approximation to account for the effect of massive neutrinos on the power spectrum. In the strongly non-linear regime, halofit systematically overpredicts the suppression due to the free streaming of the neutrinos. The maximal discrepancy occurs at k∼ 1hMpc -1, and is at the level of 10 per cent of the total suppression. Most published constraints on neutrino masses based on halofit are not affected, as they rely on data probing the matter power spectrum in the linear or mildly non-linear regime. However, predictions for future galaxy, Lyman α forest and weak lensing surveys extending to more non-linear scales will benefit from the improved approximation to the non-linear matter power spectrum we provide. Our approximation reproduces the induced neutrino suppression over the targeted scales and redshifts significantly better. We test its robustness with regard to changing cosmological parameters and a variety of modelling effects. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Piersanti L.,National institute for astrophysics | Piersanti L.,National Institute of Nuclear Physics, Italy | Tornambe A.,National institute for astrophysics | Yungelson L.R.,Institute of Astronomy
Monthly Notices of the Royal Astronomical Society | Year: 2014

The behaviour of carbon-oxygen (CO) white dwarfs (WDs) subject to direct helium accretion is extensively studied. We aim to analyse the thermal response of an accreting WD to mass deposition at different timescales. The analysis has been performed for initialWD masses and accretion rates in the range 0.60-1.02 M⊙ and 10-9-10-5 M⊙ yr-1, respectively. Thermal regimes in the parameter space MWD- MHe leading to formation of red-giant-like structures, steady burning of He, and mild, strong and dynamical flashes have been identified and the transition between these regimes has been studied in detail. In particular, the physical properties of WDs experiencing the He-flash accretion regime have been investigated to determine the mass retention efficiency as a function of the accretor total mass and accretion rate. We also discuss to what extent the building up of a He-rich layer via H burning could be described according to the behaviour of models accreting He-rich matter directly. Polynomial fits to the obtained results are provided for use in binary population synthesis computations. Several applications for close binary systems with He-rich donors andCOWDaccretors are considered and the relevance of the results for interpreting He novae is discussed. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Despali G.,University of Padua | Giocoli C.,University of Bologna | Giocoli C.,National institute for astrophysics | Giocoli C.,National Institute of Nuclear Physics, Italy | Tormen G.,University of Padua
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a detailed analysis of dark matter halo shapes, studying how the distributions of ellipticity, prolateness and axial ratios evolve as a function of time and mass.With this purpose in mind, we analysed the results of three cosmological simulations, running an ellipsoidal halo finder to measure triaxial halo shapes. The simulations have different scales, mass limits and cosmological parameters, which allows us to ensure a good resolution and statistics in a wide mass range, and to investigate the dependence of halo properties on the cosmological model. We confirm the tendency of haloes to be prolate at all times, even if they become more triaxial going to higher redshifts. Regarding the dependence on mass, more massive haloes are also less spherical at all redshifts, since they are the most recent forming systems and so still retain memory of their original shape at the moment of collapse. We then propose a rescaling of the shape-mass relations, using the variable ν = δc/σ to represent the mass, which absorbs the dependence on both cosmology and time, allowing us to find universal relations between halo masses and shape parameters (ellipticity, prolateness and the axial ratios) which hold at any redshift. This may be very useful to determine prior distributions of halo shapes for observational studies. © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Spitoni E.,University of Trieste | Matteucci F.,University of Trieste | Matteucci F.,National institute for astrophysics | Matteucci F.,National Institute of Nuclear Physics, Italy | Sozzetti A.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

The galactic habitable zone is defined as the region with sufficient abundance of heavy elements to form planetary systems in which Earth-like planets could be born and might be capable of sustaining life, after surviving to close supernova explosion events. Galactic chemical evolution models can be useful for studying the galactic habitable zones in different systems. We apply detailed chemical evolution models including radial gas flows to study the galactic habitable zones in our Galaxy and M31. We compare the results to the relative galactic habitable zones found with 'classical' (independent ring) models, where no gas inflows were included. For both the Milky Way and Andromeda, the main effect of the gas radial inflows is to enhance the number of stars hosting a habitable planet with respect to the 'classical' model results, in the region of maximum probability for this occurrence, relative to the classical model results. These results are obtained by taking into account the supernova destruction processes. In particular, we find that in the Milky Way the maximum number of stars hosting habitable planets is at 8 kpc from the Galactic Centre, and the model with radial flows predicts a number which is 38 per cent larger than what was predicted by the classical model. For Andromeda we find that the maximum number of stars with habitable planets is at 16 kpc from the centre and that in the case of radial flows this number is larger by 10 per cent relative to the stars predicted by the classical model. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Contini E.,University of Trieste | Contini E.,National institute for astrophysics | De Lucia G.,University of Trieste | Villalobos A.,National institute for astrophysics | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We study the formation of the intracluster light (ICL) using a semi-analytic model of galaxy formation, coupled to merger trees extracted from N-body simulations of groups and clusters. We assume that the ICL forms by (1) stellar stripping of satellite galaxies and (2) relaxation processes that take place during galaxy mergers. The fraction of ICL in groups and clusters predicted by our models ranges between 10 and 40 per cent, with a large halo-to-halo scatter and no halo mass dependence. We note, however, that our predicted ICL fractions depend on the resolution: for a set of simulations with particle mass one order of magnitude larger than that adopted in the high-resolution runs used in our study, we find that the predicted ICL fractions are 30-40 per cent larger than those found in the high-resolution runs. On cluster scale, large part of the scatter is due to a range of dynamical histories, while on smaller scale it is driven by individual accretion events and stripping of very massive satellites, M* ≥ 1010.5M⊙, that we find to be the major contributors to the ICL. The ICL in our models forms very late (below z ̃ 1), and a fraction varying between 5 and 25 per cent of it has been accreted during the hierarchical growth of haloes. In agreement with recent observational measurements, we find the ICL to be made of stars covering a relatively large range of metallicity, with the bulk of them being subsolar. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Urpin V.,National institute for astrophysics | Urpin V.,National Institute of Nuclear Physics, Italy | Urpin V.,RAS Ioffe Physical - Technical Institute
Astronomy and Astrophysics | Year: 2012

Context. Magnetohydrodynamic (MHD) instabilities can play an important role in the structure and dynamics of the pulsar magnetosphere. Aims. We consider the instability caused by differential rotation that is suggested by many theoretical models. Methods. Stability is considered by means of a linear analysis within the frame of the force-free MHD. Results. We argue that differentially rotating magnetospheres are unstable for any particular geometry of the magnetic field and rotation law. The characteristic growth time of instability is of the order of the rotation period. The instability can lead to fluctuations of the emission and enhancement of diffusion in the magnetosphere. © 2012 ESO.