National institute for astrophysics
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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Maoz D.,Tel Aviv University | Mannucci F.,National institute for astrophysics | Nelemans G.,Radboud University Nijmegen | Nelemans G.,Catholic University of Leuven
Annual Review of Astronomy and Astrophysics | Year: 2014

Type Ia supernovae (SNe Ia) are important distance indicators, element factories, cosmic-ray accelerators, kinetic-energy sources in galaxy evolution, and end points of stellar binary evolution. It has long been clear that a SN Ia must be the runaway thermonuclear explosion of a degenerate carbon-oxygen stellar core, most likely a white dwarf (WD). However, the specific progenitor systems of SNe Ia, and the processes that lead to their ignition, have not been identified. Two broad classes of progenitor binary systems have long been considered: single-degenerate (SD), in which a WD gains mass from a nondegenerate star; and double-degenerate (DD), involving the merger of two WDs. New theoretical work has enriched these possibilities with some interesting updates and variants. We review the significant recent observational progress in addressing the progenitor problem. We consider clues that have emerged from the observed properties of the various proposed progenitor populations, from studies of SN Ia sites pre- and postexplosion from analysis of the explosions themselves and from the measurement of event rates. The recent nearby and well-studied event, SN 2011fe, has been particularly revealing. The observational results are not yet conclusive and sometimes prone to competing theoretical interpretations. Nevertheless, it appears that DD progenitors, long considered the underdog option, could be behind some, if not all, SNe Ia. We point to some directions that may lead to future progress. Copyright © 2014 by Annual Reviews.

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

We constrain the neutrino properties in f(R) gravity using the latest observations from cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements. We first constrain separately the total mass of neutrinos Σmν and the effective number of neutrino species Neff. Then we constrain Neff and Σmν simultaneously. We find Σmν<0.462 eV at a 95% confidence level for the combination of Planck CMB data, WMAP CMB polarization data, BAO data, and high-l data from the Atacama Cosmology Telescope and the South Pole Telescope. We also find Neff=3.32-0.51+0.54 at a 95% confidence level for the same data set. When constraining Neff and Σm ν simultaneously, we find Neff=3.58-0.69+0.72 and Σmν<0.860 eV at a 95% confidence level, respectively. © 2013 American Physical Society.

Lanza A.F.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Context. Late-type stars interact with their close-in planets through their coronal magnetic fields. Aims. We introduce a theory for the interaction between the stellar and planetary fields focussing on the processes that release magnetic energy in the stellar coronae. Methods. We consider the energy dissipated by the reconnection between the stellar and planetary magnetic fields as well as that made available by the modulation of the magnetic helicity of the coronal field produced by the orbital motion of the planet. We estimate the powers released by both processes in the case of axisymmetric and non-axisymmetric, linear and non-linear force-free coronal fields finding that they scale as B 0 4/3 B p0 2/3 R p 2 v rel, where B 0 is the mean stellar surface field, B p0 the planetary field at the poles, R p the radius of the planet, and v rel the relative velocity between the stellar and the planetary fields. Results. A chromospheric hot spot or a flaring activity phased to the orbital motion of the planet are found only when the stellar field is axisymmetric. In the case of a non-axisymmetric field, the time modulation of the energy release is multiperiodic and can be easily confused with the intrinsic stellar variability. We apply our theory to the systems with some reported evidence of star-planet magnetic interaction finding a dissipated power at least one order of magnitude smaller than that emitted by the chromospheric hot spots. The phase lags between the planets and the hot spots are reproduced by our models in all the cases except for υ And. Conclusions. The chromospheric hot spots rotating in phase with the planets cannot be explained by the energy dissipation produced by the interaction between stellar and planetary fields as considered by our models and require a different mechanism. © 2012 ESO.

Tavecchio F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2014

The peculiar high-energy emission spectrum of the so-called extreme BL Lacs (EHBL) challenges the standard emission models of blazars. Among the possible solutions, the so-called hadronic cascade scenario assumes that the observed high-energy radiation is produced in the intergalactic space through photo-hadronic reactions by ultra-high energy cosmic rays (UHECR) with energies up to 1019-20 eV beamed by the blazar jet. Under the assumption - implicit in this model - that the intrinsic high-energy synchrotron self-Compton emission of the blazar does not substantially contribute to the observed γ-ray spectrum, we derive constraints to the basic physical quantities of the jet and we compare them with the requirements of the hadronic cascade scenario. We found that, for a plausible range of relativistic jet Doppler factors (δ = 10-50), the maximum achievable energy of the accelerated protons can exceed 2 × 1019 eV with jet powers of the order of ≈1044 erg s-1, parameters compatible with the requests of the hadronic scenario even if EHBL are embedded in magnetic fields of cosmic filaments. We also discuss the consequences of our results for the possibility that local EHBL contribute to the observed UHECR. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.

Andreon S.,National institute for astrophysics
Astronomy and Astrophysics | Year: 2012

Estimates of cosmological parameters using galaxy clusters have the scatter in the observable at a given mass as a fundamental parameter. This work computes the amplitude of the scatter for a newly introduced mass proxy, the product of the cluster total luminosity times the mass-to-light ratio, usually referred as stellar mass. The analysis of 12 galaxy clusters with excellent total masses shows a tight correlation between the stellar mass, or stellar fraction, and total mass within r500 with negligible intrinsic scatter: the 90% upper limit is 0.06 dex, the posterior mean is 0.027 dex. This scatter is similar to the one of best-determined mass proxies, such as Y X, i.e. the product of X-ray temperature, and gas mass. The size of the cluster sample used to determine the intrinsic scatter is small, as in previous works proposing low-scatter proxies because very accurate masses are needed to infer very small values of intrinsic scatter. Three-quarters of the studied clusters have lgM â‰2; 14 M⊙, which is advantageous from a cosmological perspective because these clusters are far more abundant than more massive clusters. At the difference of other mass proxies such as YX, stellar mass can be determined with survey data up to at least z = 0.9 using upcoming optical near-infrared surveys, such as DES and Euclid, or even with currently available surveys, covering however smaller solid angles. On the other end, the uncertainty about the predicted mass of a single cluster is large, 0.21 to 0.32 dex, depending on cluster richness. This is largely because the proxy itself has ≈ 0.10 dex errors for clusters of lgM ≲ 14 M⊙ mass. © ESO, 2012.

Greggio L.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

This paper investigates the possible systematic difference of type Ia supernovae (SNe Ia) properties related to the age and masses of the progenitors that could introduce a systematic bias between low- and high-redshift SNe Ia. The relation between the main features of the distribution of delay times and the masses of the progenitors is illustrated for the single (SD) and double degenerate (DD) models. Mixed models, which assume contributions from both the SD and DD channels, are also presented and tested versus the observed correlations between the SN Ia rates and the parent galaxy properties. It is shown that these correlations can be accounted for with both single-channel and mixed models, and that the rate in S0 and E galaxies may effectively provide clues on the contribution of SD progenitors to late epoch explosions. A wide range of masses for the CO white dwarf at the start of accretion is expected in almost all galaxy types; only in galaxies of the earliest types are the properties of the progenitors expected to be more uniform. For mixed models, late-type galaxies should host SD and DD explosions in comparable fractions, while in early-type galaxies DD explosions should largely prevail. Events hosted by star-forming galaxies span a wide range of delay times; prompt events could dominate only in the presence of a strong starburst. It is concluded that nearby SN Ia samples should well include the young, massive and hot progenitors that necessarily dominate at high redshift. © 2010 The Author. Journal compilation © 2010 RAS.

Andreon S.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

The analysis of a sample of 52 clusters with precise and hypothesis-parsimonious measurements of mass, derived from caustics based on about 208 member velocities per cluster on average, shows that low-mass clusters and groups are not simple scaled-down versions of their massive cousins in terms of stellar content: lighter clusters have more stars per unit cluster mass. The same analysis also shows that the stellar content of clusters and groups displays an intrinsic spread at a given cluster mass, i.e. clusters are not similar to each other in the amount of stars they contain, not even at a fixed cluster mass. The stellar mass fraction depends on halo mass with (logarithmic) slope -0.55 ± 0.08 and with 0.15 ± 0.02 dex of intrinsic scatter at a fixed cluster mass. These results are confirmed by adopting masses derived from velocity dispersion. The intrinsic scatter at a fixed cluster mass we determine for gas mass fractions taken from literature is smaller, 0.06 ± 0.01 dex. The intrinsic scatter in both the stellar and gas mass fractions is a distinctive signature that individual regions from which clusters and groups collected matter, a few tens of Mpc wide, are not yet representative of the mean gas and baryon content of the Universe. The observed stellar mass fraction values are in marked disagreement with gasdynamics simulations with cooling and star formation of clusters and groups. Instead, the amplitude and cluster mass dependency of observed stellar mass fractions are those required not to need any active galactic nuclei (AGN) feedback to describe gas and stellar mass fractions and X-ray scale relations in simple semi-analytic cluster models. By adding stellar and gas masses and accounting for the intrinsic variance of both quantities, we found that the baryon fraction is fairly constant for clusters and groups with masses between 1013.7 and 1015.0 M⊙ and it is offset from the WMAP-derived value by about 6σ. The offset is unlikely to be due to an underestimate of the stellar mass fraction, and could be related to the possible non-universality of the baryon fraction, pointed out by our measurements of the intrinsic scatter. Our analysis is the first that does not assume that clusters are identically equal at a given halo mass and it is also more accurate in many aspects. The data and code used for the stochastic computation are distributed with the paper. © 2010 The Author. Journal compilation © 2010 RAS.

He J.-H.,National institute for astrophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

In this work, we further investigate the family of f(R) dark energy models that can exactly mimic the same background expansion history as that of the ΛCDM model. We study the large scale structure in the f(R) gravity using the full set cosmological perturbation equations. We investigate the structure formation in both the spatially flat and curved universe. We also confront our model with the latest observations and conduct a Markov chain Monte Carlo analysis on the parameter space. © 2012 American Physical Society.

Galli D.,National institute for astrophysics | Palla F.,National institute for astrophysics
Annual Review of Astronomy and Astrophysics | Year: 2013

Within the precise cosmological framework provided by the Λ-cold dark matter model and standard Big Bang nucleosynthesis, the chemical evolution of the pregalactic gas can now be followed with accuracy limited only by the uncertainties on the reaction rates. Starting during the recombination era, the formation of the first molecules and molecular ions containing hydrogen, deuterium, helium, and lithium was severely hindered by the low density of the expanding Universe, the intensity of the cosmic radiation field, and the absence of solid catalyzers. Molecular hydrogen and deuterated hydrogen, the most abundant species formed in the gas phase prior to structure formation, played a fundamental role in the cooling of the gas clouds that gave birth to the first stellar generation, contributing to determine the scale of fragmentation. Primordial molecules also interacted with the photons of the cosmic background via resonant scattering, absorption, and emission. In this review, we examine the current status of the chemistry of the early Universe and discuss the most relevant reactions for which uncertainties still exist from theory or laboratory experiments. The prospects for detecting spectral distortions or spatial anisotropies due to the first atoms and molecules are also addressed. Copyright ©2013 by Annual Reviews. All rights reserved.

Vazza F.,National institute for astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2011

A flat distribution of low gas entropy in the core region of galaxy clusters is a feature commonly found in Eulerian cosmological simulations, at variance with most standard simulations of smoothed particle hydrodynamics fashion. From the literature, it is still unclear whether this difference is entirely due to numerical artefacts (e.g. spurious transfer from gravitational energy to thermal energy), physical mechanisms (e.g. enhanced mixing in Eulerian codes) or a mixture of both. This issue is related to many still open lines of research in the characterization of the dynamical evolution of the baryons in galaxy clusters: the origin of the cool-core/non-cool-core bi-modality, the diffusion of metals within galaxy clusters, the interplay between active galactic nuclei (AGN) and the intra-cluster medium, etc.In this work, we aim at constraining to what extent the entropy core is affected by numerical effects, and which are the physical reasons for its production in cosmological runs. To this end, we run a set of 30 high-resolution re-simulations of a ~3 × 10 14 M ȯ h -1 cluster of galaxies with a quiet dynamical history, using modified versions of the cosmological adaptive mesh refinement code enzo and investigating many possible (physical and numerical) details involved in the production of entropy in simulated galaxy clusters.We report that the occurrence of a flat entropy core in the innermost region of a massive cluster is mainly due to hydrodynamical processes resolved by the numerical code (e.g. shocks and mixing motions) and that additional spurious effects of numerical origin (e.g. artificial heating due to softening effects) affect the size and level of the entropy core only in a minor way.Using Lagrangian tracers we show that the entropy profile of non-radiative simulations is produced by a mechanism of 'sorting in entropy' which takes place with regularity during the cluster evolution. The evolution of tracers illustrates that the flat entropy core is caused by physical mixing of subsonic motions (mostly driven by accreted sub-clumps) within the shallow inner cluster potential.Several re-simulations were also produced for the same cluster object with the addition of radiative cooling, uniform pre-heating at high redshift (z= 10) and late (z < 1) thermal energy feedback from AGN activity in the cluster, in order to assess the effects of such mechanisms on the final entropy profile of the cluster. We report on the infeasibility of balancing the catastrophic cooling (and recovering a flat entropy profile) by means of the investigated trials for AGN activity alone, while for a sub-set of pre-heating models, or AGN feedback plus pre-heating models, a flat entropy distribution similar to non-radiative runs can be obtained with a viable energy requirement. Complementary analysis is presented also for a major merger cluster, obtaining similar results and achieving a generally good consistency with X-ray data for the entropy distribution in real galaxy clusters. © 2010 The Author. Journal compilation © 2010 RAS.

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