DellUniversity Trieste

Trieste, Italy

DellUniversity Trieste

Trieste, Italy
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Barrena R.,Institute of Astrophysics of Canarias | Barrena R.,University of La Laguna | Girardi M.,DellUniversity Trieste | Girardi M.,National institute for astrophysics | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We aim to review the internal structure and dynamics of the Abell 1351 cluster, shown to host a radio halo with a quite irregular shape. Our analysis is based on radial velocity data for 135 galaxies obtained at the Telescopio Nazionale Galileo.We combine galaxy velocities and positions to select 95 cluster galaxy members and analyse the internal dynamics of the whole cluster. We also examine X-ray data retrieved from Chandra and XMM archives. We measure the cluster redshift, (Z)=0.325, the line-of-sight (LOS) velocity dispersion, σV ~1500 km s-1, and the X-ray temperature, kT ~ 9 keV. From both X-ray and optical data independently, we estimate a large cluster mass, in the 1-4 ×1015 h -1 70 M( range. We attribute the extremely high value of σV to the bimodality in the velocity distribution.We find evidence of a significant velocity gradient and optical 3D substructure. The X-ray analysis also shows many features in favour of a complex cluster structure, probably supporting an ongoing merger of substructures in Abell 1351. The observational scenario agrees with the presence of two main subclusters in the northern region, each with its brightest galaxy (BCG1 and BCG2), detected as the two most important X-ray substructures with a rest-frame LOS velocity difference of δVrf ~ 2500 km s-1 and probably being in large part aligned with the LOS. We conclude that Abell 1351 is a massive merging cluster. The details of the cluster structure allow us to interpret the quite asymmetric radio halo as a 'normal' halo plus a southern relic, strongly supporting a previous suggestion based only on inspection of radio and preliminary X-ray data. © 2014 The Authors.

Barrena R.,Institute of Astrophysics of Canarias | Barrena R.,University of La Laguna | Girardi M.,dellUniversity Trieste | Girardi M.,National institute for astrophysics | Boschin W.,Fundacion G. Galilei INAF Telescopio Nazionale Galileo
Monthly Notices of the Royal Astronomical Society | Year: 2013

We analyse the dynamical state of Abell 1914, a merging cluster hosting a radio halo, quite unusual for its structure. Our study considers spectroscopic data for 119 galaxies obtained with the Italian Telescopio Nazionale Galileo. We select 89 cluster members from spatial and velocity distributions. We also use photometry Canada-France-Hawaii Telescope archives. Wecompute the mean cluster redshift,〈z〉 = 0.168, and the velocity dispersion which shows a high value, σV = 1210+125 -110 km s-1. From the 2D analysis we find that Abell 1914 has a northeast (NE)-south-west (SW) elongated structure with two galaxy clumps, that mostly merge in the plane of the sky. Our best but very uncertain estimate of the velocity dispersion of the main system is σV, main ~ 1000 km s-1. We estimate a virial mass Msys = 1.4-2.6×1015 h -1 70 M⊙ for the whole system. We study the merger through a simple two-body model and find that data are consistent with a bound, outgoing substructure observed just after the core crossing. By studying the 2D distribution of the red galaxies, photometrically selected, we showthat Abell 1914 is contained in a rich large-scale structure, with two close companion galaxysystems, known to be at z ~ 0.17. The system at SW supports the idea that the cluster is accreting groups from a filament aligned in the NE-SW direction, while that at NW suggests a second direction of the accretion (NW-SE). We conclude that Abell 1914 well fits among typical clusters with radio haloes. We argue that the unusual radio emission is connected to the complex cluster accretion and suggest that Abell 1914 resembles the well-known nearby merging cluster Abell 754 for its particular observed phenomenology.© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Young A.H.,University of Pennsylvania | Young A.H.,NASA | Mroczkowski T.,U.S. Navy | Romero C.,U.S. National Radio Astronomy Observatory | And 20 more authors.
Astrophysical Journal | Year: 2015

We present high resolution (9″) imaging of the Sunyaev-Zel'dovich Effect (SZE) toward two massive galaxy clusters, MACS J0647.7+7015 (z = 0.591) and MACS J1206.2-0847 (z = 0.439). We compare these 90 GHz measurements, taken with the Multiplexed Squid/TES Array at Ninety Gigahertz (MUSTANG ) receiver on the Green Bank Telescope, with generalized Navarro-Frenk-White (gNFW) models derived from Bolocam 140 GHz SZE data as well as maps of the thermal gas derived from Chandra X-ray observations. We adopt a serial-fitting approach, in which gNFW models are first fit to the Bolocam data and then compared to the MUSTANG data to determine an overall best-fit model. For MACS J0647.7+7015, we find a gNFW profile with core slope parameter γ = 0.9 fits the MUSTANG image with and probability to exceed (PTE) = 0.34. For MACS J1206.2-0847, we find , , and PTE = 0.70. In addition, we find a significant (>3σ) residual SZE feature in MACS J1206.2-0847 coincident with a group of galaxies identified in Very Large Telescope data and filamentary structure found in a weak-lensing mass reconstruction. We suggest the detected sub-structure may be the SZE decrement from a low mass foreground group or an infalling group. Giant Metrewave Radio Telescope measurements at 610 MHz reveal diffuse extended radio emission to the west, which we posit is either an active galactic nucleus-driven radio lobe, a bubble expanding away from disturbed gas associated with the SZE signal, or a bubble detached and perhaps re-accelerated by sloshing within the cluster. Using the spectroscopic redshifts available, we find evidence for a foreground (z = 0.423) or infalling group, coincident with the residual SZE feature. © 2015. The American Astronomical Society. All rights reserved..

Barai P.,National institute for astrophysics | Viel M.,National institute for astrophysics | Viel M.,National Institute of Nuclear Physics, Italy | Murante G.,National institute for astrophysics | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We investigate two modes of coupling the feedback energy from a central active galacticnucleus (AGN) to the neighbouring gas in galaxy simulations: kinetic - velocity boost andthermal - heating. We formulate kinetic feedback models for energy-driven wind (EDW)and momentum-driven wind (MDW), using two free parameters: feedback efficiency εf and AGN wind velocity ν w. A novel numerical algorithm is implemented in the smoothed particlehydrodynamics code GADGET-3, to prevent the expansion of a hole in the gas distributionaround the black hole (BH). We perform simulations of isolated evolution and merger ofdisc galaxies, of Milky Way mass as well as lower and higher masses. We find that in theisolated galaxy BH kinetic feedback generates intermittent bipolar jet-like gas outflows. Weinfer that current prescriptions for BH subgrid physics in galaxy simulations can grow theBH to observed values even in an isolated disc galaxy. The BH growth is enhanced in agalaxy merger, which consequently requires different model parameters to fit the observationsthan an isolated case. Comparing the [MBH-σ*] relation obtained in our simulations withobservational data, we conclude that it is possible to find parameter sets for a fit in all themodels (e.g. νw = 10 000 km s-1 and εf = 0.25 for BH kinetic EDW), except for the casewith MDW feedback in a galaxy merger, in which the BH is always too massive. The BHthermal feedback implementation of Springel et al. within the multiphase star formation modelis found to have negligible impact on gas properties, and the effect claimed in all previousstudies is attributed to gas depletion around the BH by the creation of an artificial hole. TheBH mass accretion rate in our simulations exhibit heavy fluctuations. The star formation rate isquenched with feedback by removal of gas. The circumgalactic medium gas at galactocentricdistances (20-100) h-1 kpc is found to give the best metallicity observational diagnostic todistinguish between BH models. © 2013 The Authors.

Nicastro F.,National institute for astrophysics | Nicastro F.,Harvard - Smithsonian Center for Astrophysics | Elvis M.,Harvard - Smithsonian Center for Astrophysics | Krongold Y.,National Autonomous University of Mexico | And 15 more authors.
Astrophysical Journal | Year: 2013

We present the first results from our pilot 500 ks Chandra Low Energy Transmission Grating Large Program observation of the soft X-ray brightest source in the z ≳ 0.4 sky, the blazar 1ES 1553+113, aimed to secure the first uncontroversial detections of the missing baryons in the X-rays. We identify a total of 11 possible absorption lines, with single-line statistical significances between 2.2σ and 4.1σ. Six of these lines are detected at high single-line statistical significance (3.6 ≤ σ ≤ 4.1), while the remaining five are regarded as marginal detections in association with either other X-ray lines detected at higher significance and/or far-ultraviolet (FUV) signposts. Three of these lines are consistent with metal absorption at z ≃ 0, and we identify them with Galactic O I and C II. The remaining eight lines may be imprinted by intervening absorbers and are all consistent with being high-ionization counterparts of FUV H I and/or O VI intergalactic medium signposts. In particular, five of these eight possible intervening absorption lines (single-line statistical significances of 4.1σ, 4.1σ, 3.9σ, 3.8σ, and 2.7σ), are identified as C V and C VI Kα absorbers belonging to three WHIM systems at zX = 0.312, z X = 0.237, and 〈zX 〉 = 0.133, which also produce broad H I (and O VI for the zX = 0.312 system) absorption in the FUV. For two of these systems (zX = 0.312 and 0.237), the Chandra X-ray data led the a posteriori discovery of physically consistent broad H I associations in the FUV (for the third system the opposite applies), so confirming the power of the X-ray-FUV synergy for WHIM studies. The true statistical significances of these three X-ray absorption systems, after properly accounting for the number of redshift trials, are 5.8σ (z X = 0.312; 6.3σ if the low-significance O V and C V Kβ associations are considered), 3.9σ (zX = 0.237), and 3.8σ (〈zX 〉 = 0.133), respectively. © 2013. The American Astronomical Society. All rights reserved.

Marenzana M.,Imperial College London | Marenzana M.,University of Oxford | Hagen C.K.,University College London | Das Neves Borges P.,Imperial College London | And 7 more authors.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014

The mouse model of osteoarthritis (OA) has been recognized as the most promising research tool for the identification of new OA therapeutic targets. However, this model is currently limited by poor throughput, dependent on the extremely timeconsuming histopathology assessment of the articular cartilage (AC). We have recently shown that AC in the rat tibia can be imaged both in air and in saline solution using a laboratory system based on coded-aperture X-ray phase-contrast imaging (CAXPCi). Here, we explore ways to extend the methodology for imaging the much thinner AC of the mouse, by means of gold-standard synchrotronbased phase-contrast methods. Specifically, we have used analyser-based phase-contrast micro-computed tomography (micro-CT) for its high sensitivity to faint phase changes, coupled with a high-resolution (4.5μm pixel) detector. Healthy, diseased (four weeks post induction of OA) and artificially damaged mouse AC was imaged at the Elettra synchrotron in Trieste, Italy, using the above method. For validation, we used conventional micro-CT combined with radiopaque soft-tissue staining and standard histomorphometry. We show that mouse cartilage can be visualized correctly by means of the synchrotron method. This suggests that: (i) further developments of the laboratory-based CAXPCi system, especially in terms of pushing the resolution limits, might have the potential to resolve mouse AC ex vivo and (ii) additional improvements may lead to a new generation of CAXPCi micro-CT scanners which could be used for in vivo longitudinal pre-clinical imaging of soft tissue at resolutions impossible to achieve by current MRI technology. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Calucci G.,DellUniversity Trieste | Treleani D.,DellUniversity Trieste
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Multiple Parton Interactions are the tool to obtain information on the correlations between partons in the hadron structure. Partons may be correlated in all degrees of freedom and all different correlation terms contribute to the cross section. The contributions due to the different parton flavors can be isolated, at least to some extent, by selecting properly the final state. In the case of high energy proton-proton collisions, the effects of correlations in the transverse coordinates and in fractional momenta are, on the contrary, unavoidably mixed in the final observables. The standard way to quantify the strength of double parton interactions is by the value of the effective cross section and a small value of the effective cross section may be originated both by the relatively short transverse distance between the pairs of partons undergoing the double interaction and by a large dispersion of the distribution in multiplicity of the multiparton distributions. The aim of the present paper is to show how the effects of longitudinal and transverse correlations may be disentangled by taking into account the additional information provided by double parton interactions in high energy proton-deuteron collisions.© 2011 American Physical Society.

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