S. Andreon

The XMM-LSS survey. Survey design and first results

We have designed a medium deep large area X-ray survey with XMM - the XMM Large Scale Structure survey, XMM-LSS - with the scope of extending the cosmological tests attempted using ROSAT cluster samples to two redshift bins between 0

The scaling relation between richness and mass of galaxy clusters: a Bayesian approach

We use a sample of 53 galaxy clusters at 0.03 < z < 0.1 with available masses derived from the caustic technique and with velocity dispersions computed using 208 galaxies on average per cluster, in order to investigate the scaling between richness, mass and velocity dispersion. A tight scaling between richness and mass is found, with an intrinsic scatter of only 0.19 dex in mass and with a slope one, i.e. clusters that have twice as many galaxies are twice as massive. When richness is measured without any knowledge of the cluster mass or linked parameters (such as r(200)), it can predict mass with an uncertainty of 0.29 +/- 0.01 dex. As a mass proxy, richness competes favourably with both direct measurements of mass given by the caustic method, which has typically 0.14 dex errors (versus 0.29) and X-ray luminosity, which offers a similar 0.30 dex uncertainty. The similar performances of X-ray luminosity and richness in predicting cluster masses has been confirmed using cluster masses derived from velocity dispersion fixed by numerical simulations. These results suggest that cluster masses can be reliably estimated from simple galaxy counts, at least at the redshift and masses explored in this work. This has important applications in the estimation of cosmological parameters from optical cluster surveys, because in current surveys clusters detected in the optical range outnumber, by at least one order of magnitude, those detected in X-ray. Our analysis is robust from an astrophysical perspective because the adopted masses are among the most hypothesis-parsimonious estimates of cluster mass and from a statistical perspective, because our Bayesian analysis accounts for terms usually neglected, such as the Poisson nature of galaxy counts, the intrinsic scatter and uncertain errors. The data and code used for the stochastic computation are provided in the paper.

The VISTA Deep Extragalactic Observations (VIDEO) survey

In this paper we describe the first data release of the the Visible andnInfrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observationsn(VIDEO) survey. VIDEO is a ~12degree^2 survey in the near-infrared Z,Y,J,H andnK_s bands, specifically designed to enable the evolution of galaxies and largenstructures to be traced as a function of both epoch and environment from thenpresent day out to z=4, and active galactic nuclei (AGN) and the most massivengalaxies up to and into the epoch of reionization. With its depth and area,nVIDEO will be able to fully explore the period in the Universe where AGN andnstarburst activity were at their peak and the first galaxy clusters werenbeginning to virialize. VIDEO therefore offers a unique data set with which toninvestigate the interplay between AGN, starbursts and environment, and the rolenof feedback at a time when it was potentially most crucial.n We provide data over the VIDEO-XMM3 tile, which also covers thenCanada-France-Hawaii-Telescope Legacy Survey Deep-1 field (CFHTLS-D1). Thenreleased VIDEO data reach a 5-sigma AB-magnitude depth of Z=25.7, Y=24.5,nJ=24.4, H=24.1 and K_s=23.8 in 2 arcsec diameter apertures (the full depth ofnY=24.6 will be reached within the full integration time in future releases).nThe data are compared to previous surveys over this field and we find goodnastrometric agreement with the Two-Micron All Sky Survey, and source counts innagreement with the recently released UltraVISTA survey data. The addition ofnthe VIDEO data to the CFHTLS-D1 optical data increases the accuracy ofnphotometric redshifts and significantly reduces the fraction of catastrophicnoutliers over the redshift range 0

XMM-LSS discovery of a z= 1.22 galaxy cluster

We present details of the discovery of XLSS J022303.0−043622, a z= 1.2 cluster of galaxies. This cluster was identified from its X-ray properties and selected as a z > 1 candidate from its optical/near-infrared (IR) characteristics in the XMM Large-Scale Structure Survey (XMM-LSS). It is the most distant system discovered in the survey to date. We present ground-based optical and near-IR observations of the system carried out as part of the XMM-LSS survey. The cluster has a bolometric X-ray luminosity of 1.1 ± 0.7 × 10^44 erg s^−1 , fainter than most other known z > 1 X-ray selected clusters. In the optical it has a remarkably compact core, with at least a dozen galaxies inside a 125 kpc radius circle centred on the X-ray position. Most of the galaxies within the core, and those spectroscopically confirmed to be cluster members, have stellar masses similar to those of massive cluster galaxies at low redshift. They have colours comparable to those of galaxies in other z > 1 clusters, consistent with showing little sign of strong ongoing star formation. The bulk of the star formation within the galaxies appears to have ceased at least 1.5 Gyr before the observed epoch. Our results are consistent with massive cluster galaxies forming at z > 1 and passively evolving thereafter. We also show that the system is straightforwardly identified in Spitzer/IRAC 3.6- and 4.5-μm data obtained by the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey emphasizing the power and utility of joint XMM and Spitzer searches for the most distant clusters.

Rigorous luminosity function determination in the presence of a background: theory and application to two intermediate redshift clusters★

In this paper we present a rigorous derivation of the luminosity function (LF) in the presence of a background. Our approach is free from the logical contradictions of assigning negative values to positively defined quantities and avoids the use of incorrect estimates for the 68 per cent confidence interval (error bar). It accounts for Poisson fluctuations ignored in previous approaches and does not require binning of the data. The method is extensible to more complex situations, does not require the existence of an environment-independent LF, and clarifies issues common to field LF derivations. We apply the method to two clusters of galaxies at intermediate redshift (z ∼ 0.3) with among the deepest and widest K s observations ever taken. Finally, we point out the shortcomings of flip-flopping magnitudes.

The XMM-Large scale structure catalogue: X-ray sources and associated optical data. Version I

Following the presentation of the XMM-Large Scale Structure (XMM-LSS) survey X-ray source detection package by Pacaud et al., we provide the source lists for the first surveyed 5.5 deg 2 . The catalogues pertain to the [0.5-2] and [2-10] keV bands and contain in total 3385 point-like or extended sources above a detection likelihood of 15 in either band. The agreement with deep log N- log S is excellent. The main parameters considered are position, count rate, source extent with associated likelihood values. A set of additional quantities such as astrometric corrections and fluxes are further calculated while errors on the position and count rate are deduced from simulations. We describe the construction of the band-merged catalogue allowing rapid subsample selection and easy cross-correlation with external multiwavelength catalogues. A small optical Canada-France-Hawaii Telescope Legacy Survey multiband subset of objects are associated with each source along with an X-ray/optical overlay. We make the full X-ray images available in FITS format. The data are available at the Centre de Donnees de Strasbourg and, in a more extended form, at the Milan XMM-LSS survey data base.

Batch discovery of nine z ∼ 1 clusters using X-ray and K or R,z′ images

We present the results of an initial search for clusters of galaxies at z ∼ 1 and above, using data from 2.9 square degrees of XMM-Newton images. By selecting weak potentially extended X-ray sources with faint or no identifications in deep, ground-based optical imaging, we have constructed a starting sample of 19 high-redshift cluster candidates. Near-IR and R, z imaging of these fields identified nine of them as high-redshift systems. Six of these were confirmed spectroscopically, three at z ∼ 1.0 and the other three in the 0.8 < z < 0.92 range. The remaining three systems have solid photometric evidence to be at z phot ∼ 0.8, 1.0 and 1.3. The present sample significantly increases the number of such clusters. The measured density of z ≥ 1 clusters, after discarding low-redshift systems at z ≤ 0.92 is about 1.7 deg -2 (with 68 per cent confidence interval equal to [ 1.0, 2.9]) for f X ≥ 2.5 10 -15 erg cm -2 s -1 ([0.5-2] keV) and this is a lower limit, having screened not all potential z ∼ 1 candidate clusters. Coordinates, X-ray measures and evidence for nine X-ray-selected high-redshift clusters is given.

Galaxy evolution in clusters up to z= 1.0

We present a combined study of the colour-magnitude relation, colour distribution and luminosity function (LF) of a sample of 24 clusters at redshifts 0.3 < z < 1. The sample is largely composed of X-ray selected/detected clusters. Most of the clusters at redshifts z < 0.6 display X-ray luminosity or richness typical of poor clusters or groups, rather than the more typical, massive clusters studied in literature at redshifts z? 0.3. All our clusters, including groups, display a colour-magnitude relation consistent with a passively evolving stellar population formed at a redshift z f ? 2, in accordance with observed galaxy populations in more massive clusters studied at comparable redshifts. Colours and luminosity functions (LFs) show that the cluster galaxy population is consistent with the presence of at least two components: old systems formed at high redshift that have evolved passively from that epoch, together with a galaxy population displaying more recent star formation. The former population forms at 2? z f ? 5, the latter at redshifts z < 1. A model in which stars do not evolve is clearly rejected both by the colour of reddest galaxies and by the characteristic luminosity m* measures. All clusters (with one possible exception) are detected independently by an almost three-dimensional optical search employing sky position and colour - this despite the primary X-ray selection and low X-ray flux/optical richness displayed by most of the sample.

Extending the Butcher–Oemler effect up to z∼ 0.7

We have observed three clusters at z ∼ 0.7, of richness comparable to the low-redshift sample of Butcher & Oemler (BO), and have determined their fraction of blue galaxies. When adopting the standard error definition, two clusters have a low blue fraction for their redshifts, whereas the fraction of the third one is compatible with the expected value. A detailed analysis of previous BO-like studies that adopted different definitions of the blue fraction shows that the modified definitions are affected by contaminating signals: colour segregation in clusters affects blue fractions derived in fixed metric apertures, differential evolution of early and late type spirals potentially affects blue fractions derived with a non-standard choice of the colour cut, and the younger age of the universe at high redshift affects blue fractions computed with a colour cut taken relatively to a fixed non-evolving colour. Adopting these definitions, we find largely varying blue fractions. This thorough analysis of the drawbacks of the different possible definitions of the blue fraction should allow future studies to perform measures in the same scale. Finally, if one adopts a more refined error analysis to deal with BO and our data, a constant blue fraction with redshift cannot be excluded, showing that the BO effect is still far from being detected beyond doubt.

Testing the galaxy cluster mass-observable relations at z = 1 with XMM-Newton and Chandra observations of XLSSJ022403.9-041328 ⋆ .

We present an analysis of deep XMM-Newton and Chandra observations of the z = 1.05 galaxy cluster XLSSJ022403.9-041328 (hereafter XLSSC 029), detected in the XMM-Newton Large Scale Structure survey. Density and temperature profiles of the X-ray emitting gas were used to perform a hydrostatic mass analysis of the system. This allowed us to measure the total mass and gas fraction in the cluster and define overdensity radii R 500 and R 2500 . The global properties of XLSSC 029 were measured within these radii and compared with those of the local population. The gas mass fraction was found to be consistent with local clusters. The mean metal abundance was 0.18 +0.17 -0.15 Z ⊙ , with the cluster core regions excluded, consistent with the predicted and observed evolution. The properties of XLSSC 029 were then used to investigate the position of the cluster on the M-kT, Y x -M and L x -M scaling relations. In all cases the observed properties of XLSSC 029 agreed well with the simple self-similar evolution of the scaling relations. This is the first test of the evolution of these relations at z > 1 and supports the use of the scaling relations in cosmological studies with distant galaxy clusters.