Clustering of X-Ray-Selected AGN

The study of the angular and spatial structure of the X-ray sky has been under investigation since the times of the Einstein X-ray Observatory. This topic has fascinated more than two generations of scientists and slowly unveiled an unexpected scenario regarding the consequences of the angular and spatial distribution of X-ray sources. It was first established from the clustering of sources making the CXB that the source spatial distribution resembles that of optical QSO. It then it became evident that the distribution of X-ray AGN in the Universe was strongly reflecting that of Dark Matter. In particular one of the key result is that X-ray AGN are hosted by Dark Matter Halos of mass similar to that of galaxy groups. This result, together with model predictions, has lead to the hypothesis that galaxy mergers may constitute the main AGN triggering mechanism. However detailed analysis of observational data, acquired with modern telescopes, and the use of the new Halo Occupation formalism has revealed that the triggering of an AGN could also be attributed to phenomena like tidal disruption or disk instability, and to galaxy evolution. This paper reviews results from 1988 to 2011 in the field of X-ray selected AGN clustering.Comment: 19 pages, 4 Figures, review paper published on Advances in Astronomy Special Issue "Seeking for the Leading Actor on the Cosmic Stage: Galaxies versus Supermassive Black Holes", v2, final versio

Clustering of gamma-ray selected 2LAC Fermi Blazars

We present the first measurement of the projected correlation function of 485 gamma-ray selected Blazars, divided in 175 BLLacertae (BL Lacs) and 310 Flat Spectrum Radio Quasars (FSRQs) detected in the 2-year all-sky survey by Fermi-Large Area Telescope. We find that Fermi BL Lacs and FSRQs reside in massive dark matter halos (DMHs) with logMh=13.35+0.20/-0.14 and logMh = 13.40+0.15/-0.19 Msun/h, respectively, at low (z=0.4) and high (z =1.2) redshift. In terms of clustering properties, these results suggest that BL Lacs and FSRQs are similar objects residing in the same dense environment typical of galaxy groups, despite their different spectral energy distribution, power and accretion rate. We find no difference in the typical bias and hosting halo mass between Fermi Blazars and radio-loud AGN, supporting the unifcation scheme simply equating radio-loud objects with misaligned Blazar counterparts. This similarity in terms of typical environment they preferentially live in, suggests that Blazars preferentially occupy the centre of DMHs, as already pointed out for radio-loud AGN. This implies, in light of several projects looking for the gamma-ray emission from DM annihilation in galaxy clusters, a strong contamination from Blazars to the expected signal from DM annihilation.Comment: Accepted for publication in The Astrophysical Journa

XMM observation of M~87 II. Abundance structure of the interstellar and intergalactic medium

Based on a detailed study of the temperature structure of the intracluster medium in the halo of M~87, abundance profiles of 7 elements, O, Mg, Si, S, Ar, Ca, and Fe are derived. In addition, abundance ratios are derived from the ratios of line strengths, whose temperature dependences are small within the temperature range of the ICM of M~87. The abundances of Si, S, Ar, Ca and Fe show strong decreasing gradients outside 2$'$ and become nearly constant within the radius at $\sim1.5$ solar. The Fe/Si ratio is determined to be 0.9 solar with no radial gradient. In contrast, the O abundance is less than a half of the Si abundance at the center and has a flatter gradient. The Mg abundance is $\sim$1 solar within 2$'$, which is close to stellar abundance within the same radius. The O/Si/Fe pattern of M~87 is located at the simple extension of that of Galactic stars. The observed Mg/O ratio is about 1.25 solar, which is also the same ratio as for Galactic stars. The O/Si/Fe ratio indicates that the SN Ia contribution to Si and Fe becomes important towards the center and SN Ia products have similar abundances of Si and Fe at least around M~87, which may reflect dimmer SN Ia observed in old stellar systems. The S abundance is similar to the Si abundance at the center, but has a steeper gradient. This result suggests that the S/Si ratio of SN II products is much smaller than the solar ratio.Comment: 20 pages, 20 figures, to appear in Astronomy & Astrophysic

New Test of the Friedmann-Lemaitre-Robertson-Walker Metric Using the Distance Sum Rule

We present a new test of the validity of the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric, based on comparing the distance from redshift 0 to z(1) and from z(1) to z(2) to the distance from 0 to z(2). If the Universe is described by the FLRWmetric, the comparison provides a model-independent measurement of spatial curvature. The test relies on geometrical optics, it is independent of the matter content of the Universe and the applicability of the Einstein equation on cosmological scales. We apply the test to observations, using the Union2.1 compilation of supernova distances and Sloan Lens ACS Survey galaxy strong lensing data. The FLRW metric is consistent with the data, and the spatial curvature parameter is constrained to be -1.22 <Omega(K0) <0.63, or -0.08 <Omega(K0) <0.97 with a prior from the cosmic microwave background and the local Hubble constant, though modeling of the lenses is a source of significant systematic uncertainty.Peer reviewe

THE ELEVENTH AND TWELFTH DATA RELEASES OF THE SLOAN DIGITAL SKY SURVEY : FINAL DATA FROM SDSS-III

The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All of the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 deg(2) of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include the measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 deg(2) of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 deg(2); 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra.Peer reviewe

Possible AGN Shock Heating in the Cool Core Galaxy Cluster Abell 478

We present a detailed X-ray study of the intracluster medium (ICM) of the nearby, cool-core galaxy cluster Abell 478, with Chandra and XMM observations. Using a wavelet smoothing hardness analysis, we derive detailed temperature maps of A478, revealing a surprising amount of temperature structure. The broad band Chandra spectral fits yield temperatures which are significantly hotter than those from XMM, but the Fe ionization temperature shows good agreement. We show that the temperature discrepancy is slightly reduced when comparing spectra from regions selected to enclose nearly isothermal gas. However, by simulating multi-temperature spectra and fitting them with a single temperature model, we find no significant difference between Chandra and XMM, indicating that non-isothermality cannot fully explain the discrepancy. We have discovered 4 hot spots located between 30--50 kpc from the cluster center, where the gas temperature is roughly a factor of 2 higher than in the surrounding material. We estimate the combined excess thermal energy present in these hot spots to be (3+/-1)x10^59 erg. The location of and amount of excess energy present in the hot spots are suggestive of a common origin within the cluster core, which hosts an active galactic nucleus. This cluster also possesses a pair of X-ray cavities coincident with weak radio lobes, as reported in a previous analysis, with an associated energy <10% of the thermal excess in the hot spots. The presence of these hot spots could indicate strong-shock heating of the ICM from the central radio source -- one of the first such detections in a cool core cluster. We also probe the mass distribution in the core and find it to be characterized by a logarithmic slope of -0.35+/-0.22, which is significantly flatter than an NFW cusp of -1. (abridged)Comment: 15 pages, 15 figures; extra section on simulating effect of multiphase gas, plus some restructuring of discussion section. Accepted by ApJ; corrected typo in equation

A Deficit of Faint Red Galaxies in the Possible Large-Scale Structures around the RDCS J1252.9-2927 Cluster at z=1.24

(Abridged) We report a discovery of possible large-scale structures around the RDCS J1252.9-2927 cluster at z=1.24 based on photometric redshifts. We carried out multi-band wide-field imaging with Suprime-Cam on the Subaru Telescope and WFCAM on the United Kingdom Infra-Red Telescope (UKIRT). The distribution of photo-z selected galaxies reveals clumpy structures surrounding the central cluster. We compare the observed structure with an X-ray map and find that two of the four plausible clumps show significant X-ray emissions and one with a marginal detection, which strongly suggest that they are dynamically bound systems. Following the discovery of the possible large-scale structure, we carried out deeper SOFI K_s-band imaging with New Technology Telescope on the four plausible clumps. We construct the optical-to-near-infrared colour-magnitude diagrams of the galaxies in the clumps, and find that the colour-magnitude relation (CMR) of the red galaxies in the clumps is sharply truncated below K_s=22. Interestingly, the main cluster shows a clear relation down to K_s=23 (Lidman et al. 2004). We suggest that galaxies follow the 'environment-dependent down-sizing' evolution. Massive galaxies in high density environments first stop forming stars and become red. Less massive galaxies in less dense environments become red at later times. Based on a few assumptions, we predict that the brightest tip of the CMR appears at z~2.5.Comment: 10 pages, 8 figures, accepted for publication in MNRA

LoCuSS: Calibrating Mass-Observable Scaling Relations for Cluster Cosmology with Subaru Weak Lensing Observations

We present a joint weak-lensing/X-ray study of galaxy cluster mass-observable scaling relations, motivated by the critical importance of accurate calibration of mass proxies for future X-ray missions, including eROSITA. We use a sample of 12 clusters at z\simeq0.2 that we have observed with Subaru and XMM-Newton to construct relationships between the weak-lensing mass (M), and three X-ray observables: gas temperature (T), gas mass (Mgas), and quasi-integrated gas pressure (Yx) at overdensities of \Delta=2500, 1000, and 500 with respect to the critical density. We find that Mgas at \Delta\le1000 appears to be the most promising mass proxy of the three, because it has the lowest intrinsic scatter in mass at fixed observable: \sigma_lnM\simeq0.1, independent of cluster dynamical state. The scatter in mass at fixed T and Yx is a factor of \sim2-3 larger than at fixed Mgas, which are indicative of the structural segregation that we find in the M-T and M-Yx relationships. Undisturbed clusters are found to be \sim40% and \sim20% more massive than disturbed clusters at fixed T and Yx respectively at \sim2\sigma significance. In particular, A1914 - a well-known merging cluster - significantly increases the scatter and lowers the the normalization of the relation for disturbed clusters. We also investigated the covariance between intrinsic scatter in M-Mgas and M-T relations, finding that they are positively correlated. This contradicts the adaptive mesh refinement simulations that motivated the idea that Yx may be a low scatter mass proxy, and agrees with more recent smoothed particle hydrodynamic simulations based on the Millennium Simulation. We also propose a method to identify a robust mass proxy based on principal component analysis. The statistical precision of our results are limited by the small sample size and the presence of the extreme merging cluster in our sample.Comment: 13 pages, 6 figures : ApJ in press : proof ve