arXiv subjects

S. Maurogordato

Publications and source records attributed to S. Maurogordato.

At least 73 records · Page 4Linked to original sources

arXiv2018

The XXL Survey XXVIII. Galaxy luminosity functions of the XXL-N clusters

The main goal of this study is to investigate the LF of a sample of 142 X-ray selected clusters, with spectroscopic redshift confirmation and a well defined selection function, spanning a wide redshift and mass range, and to test the LF dependence on cluster global properties, in a homogeneous and unbiased way. Our study is based on the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) photometric galaxy catalogue,associated with photometric redshifts. We constructed LFs inside a scaled radius using a selection in photometric redshift around the cluster spectroscopic redshift in order to reduce projection effects. The width of the photometric redshift selection was carefully determined to avoid biasing the LF and depended on both the cluster redshift and the galaxy magnitudes. The purity was then enhanced by applying a precise background subtraction. We constructed composite luminosity functions (CLFs) by stacking the individual LFs and studied their evolution with redshift and richness, analysing separately the brightest cluster galaxy (BCG) and non-BCG members. We fitted the dependences of the CLFs and BCG distributions parameters with redshift and richness conjointly in order to distinguish between these two effects. We find that the usual photometric redshift selection methods can bias the LF estimate if the redshift and magnitude dependence of the photometric redshift quality is not taken into account. Our main findings concerning the evolution of the galaxy luminosity distribution with redshift and richness are that, in the inner region of clusters and in the redshift-mass range we probe (about $0<z<1$ and $10^{13} M_{\odot}<M_{500}<5\times10^{14}M_{\odot}$), the bright part of the LF (BCG excluded) does not depend much on mass or redshift except for its amplitude, whereas the BCG luminosity increases both with redshift and richness, and its scatter decreases with redshift.

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arXiv2018

The XXL Survey: XXX. Characterisation of the XLSSsC N01 supercluster and analysis of the galaxy stellar populations

Superclusters form from the largest enhancements in the primordial density perturbation field and extend for tens of Mpc, tracing the large-scale structure of the Universe. We characterise XLSSsCN01, a rich supercluster at z~0.3 detected in the XXL Survey, composed of X-ray clusters of different virial masses and luminosities. As one of the first studies on this topic, we investigate the stellar populations of galaxies in different environments in the supercluster region. We study a magnitude-limited (r<=20) and a mass-limited sample (log(M*/M_sun)>10.8) of galaxies in the virialised region and in the outskirts of 11 XLSSsCN01 clusters, in high- and low-density field. We compute the stellar population properties of galaxies using spectral energy distribution and spectral fitting techniques, and study the dependence of star formation rates (SFR), colours, and stellar ages on environment. For r<20, the fraction of SFing/blue galaxies, computed either from the specific-SFR (sSFR) or rest-frame(rf) colour, shows depletion within the cluster virial radii, where the number of galaxies with log(sSFR/yr^-1)>-12 and with (g-r)_rf<0.6 is lower than in the field. For log(M*/M_sun)>10.8, no trends with environment emerge, as massive galaxies are mostly already passive in all environments. No differences among low- and high-density field members and cluster members emerge in the sSFR-mass relation. The luminosity-weighted age-mass relation of the passive populations within cluster virial radii show signatures of recent environmental quenching. The study of luminous and massive galaxies in this supercluster shows that while environment has a prominent role in determining the fractions of SFing/blue galaxies, its effects on the star formation activity in SFing galaxies are negligible.

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arXiv2017

Sub-structure and merger detection in resolved NIKA Sunyaev-Zel'dovich images of distant clusters

Sub-structures in the hot gas of galaxy clusters are related to their formation history and to the astrophysical processes at play in the intracluster medium (ICM). The thermal Sunyaev-Zel'dovich (tSZ) effect is directly sensitive to the line-of-sight integrated ICM pressure, and is thus particularly adapted to study ICM sub-structures. We apply structure-enhancement filtering algorithms to high resolution tSZ observations of distant clusters, in order to search for pressure discontinuities, compressions, as well as secondary peaks in the ICM. The same filters are applied to synthetic tSZ images extracted from RHAPSODY-G hydrodynamic simulations, in order to better interpret the extracted features. We also study the noise propagation trough the filters and quantify the impact of systematic effects, point source residuals being identified as the dominant potential contaminant. In 3 of our 6 NIKA clusters we identify features at high S/N that show clear evidence for merger events. In MACSJ0717 (z=0.55), three strong pressure gradients are observed on the E, SE and W sectors, and two main peaks in the pressure distribution are identified. We observe a lack of tSZ compact structure in the cool-core cluster PSZ1G045.85 (z=0.61), and a tSZ gradient ridge dominates in the SE. In the highest z cluster, CLJ1227 (z=0.89), we detect a ~45" (360 kpc) long ridge pressure gradient associated with a secondary pressure peak in the W region. Our results show that current tSZ facilities have now reached the angular resolution and sensitivity to allow an exploration of the details of pressure sub-structures in clusters, even at high z. This opens the possibility to quantify the impact of the dynamical state on the relation between the tSZ signal and the mass of clusters, which is important when using tSZ clusters to test cosmological models. This work also marks the first NIKA cluster sample data release.

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arXiv2017

The XXL Survey: XXIII. The Mass Scale of XXL Clusters from Ensemble Spectroscopy

An X-ray survey with the XMM-Newton telescope, XMM-XXL, has identified hundreds of galaxy groups and clusters in two 25 deg$^2$ fields. Combining spectroscopic and X-ray observations in one field, we determine how the kinetic energy of galaxies scales with hot gas temperature and also, by imposing prior constraints on the relative energies of galaxies and dark matter, infer a power-law scaling of total mass with temperature. Our goals are: i) to determine parameters of the scaling between galaxy velocity dispersion and X-ray temperature, $T_{\rm 300kpc}$, for the halos hosting XXL-selected clusters, and; ii) to infer the log-mean scaling of total halo mass with temperature, $\langle \ln M_{200} \, | \, T, z \rangle$. We apply an ensemble velocity likelihood to a sample of $> 1500$ spectroscopic redshifts within $132$ spectroscopically confirmed clusters with redshifts $z < 0.6$ to model, $\langle \ln σ_{\rm gal}\,|\,T,z\rangle$, where $σ_{\rm gal}$ is the velocity dispersion of XXL cluster member galaxies and $T$ is a 300 kpc aperture temperature. To infer total halo mass we use a precise virial relation for massive halos calibrated by N-body simulations along with a single degree of freedom summarizing galaxy velocity bias with respect to dark matter. For the XXL-N cluster sample, we find $σ_{\rm gal} \propto T^{0.63\pm0.05}$, a slope significantly steeper than the self-similar expectation of $0.5$. Assuming scale-independent galaxy velocity bias, we infer a mean logarithmic mass at a given X-ray temperature and redshift, $\langle\ln (E(z) M_{200}/10^{14}\,{\rm M}_{\odot})|T,z\rangle=π+α\ln(T/T_p )+β\ln (E(z)/E(z_p) )$ using pivot values ${\rm k}T_{p}=2.2\,{\rm keV}$ and $z_p=0.25$, with normalization $π=0.45\pm0.24$ and slope $α=1.89\pm0.15$. We obtain only weak constraints on redshift evolution, $β=-1.29\pm1.14$.

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arXiv2017

The XXL Survey: XXII. The XXL-North spectrophotometric sample and galaxy stellar mass function in X-ray detected groups and clusters

The fraction of galaxies bound in groups in the nearby Universe is high (50% at z~0). Systematic studies of galaxy properties in groups are important in order to improve our understanding of the evolution of galaxies and of the physical phenomena occurring within this environment. We have built a complete spectrophotometric sample of galaxies within X-ray detected, optically spectroscopically confirmed groups and clusters (G&C), covering a wide range of halo masses at z<= 0.6. In the context of the XXL survey, we analyse a sample of 164 G&C in the XXL-North region (XXL-N), at z <= 0.6, with a wide range of virial masses (1.24 x 10^13 <=M_500 M_sun <= 6.63 x 10^14) and X-ray luminosities ( 2.27 x 10^41 <= L^XXL_500 (erg/s)<= 2.15 x10^44). The G&C are X-ray selected and spectroscopically confirmed. We describe the membership assignment and the spectroscopic completeness analysis, and compute stellar masses. As a first scientific exploitation of the sample, we study the dependence of the galaxy stellar mass function (GSMF) on global environment. We present a spectrophotometric characterisation of the G&C and their galaxies. The final sample contains 132 G&C, 22111 field galaxies and 2225 G&C galaxies with r-band magnitude <20. Of the G&C, 95% have at least three spectroscopic members, and 70% at least ten. The shape of the GSMF seems not to depend on environment (field versus G&C) or X-ray luminosity ( used as a proxy for the virial mass of the system). These results are confirmed by the study of the correlation between mean stellar mass of G&C members and L^XXL_500.We release the spectrophotometric catalogue of galaxies with all the quantities computed in this work. As a first homogeneous census of galaxies within X-ray spectroscopically confirmed G&C at these redshifts, this sample will allow environmental studies of the evolution of galaxy properties.

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arXiv2017

Mapping the hot gas temperature in galaxy clusters using X-ray and Sunyaev-Zel'dovich imaging

We propose a method to map the temperature distribution of the hot gas in galaxy clusters that uses resolved images of the thermal Sunyaev-Zel'dovich (tSZ) effect in combination with X-ray data. Application to images from the New IRAM KIDs Array (NIKA) and XMM-Newton allows us to measure and determine the spatial distribution of the gas temperature in the merging cluster MACS J0717.5+3745, at $z=0.55$. Despite the complexity of the target object, we find a good morphological agreement between the temperature maps derived from X-ray spectroscopy only -- using XMM-Newton ($T_{\rm XMM}$) and Chandra ($T_{\rm CXO}$) -- and the new gas-mass-weighted tSZ+X-ray imaging method ($T_{\rm SZ}$). We correlate the temperatures from tSZ+X-ray imaging and those from X-ray spectroscopy alone and find that $T_{\rm SZ}$ is higher than $T_{\rm XMM}$ and lower than $T_{\rm CXO}$ by $\sim 10\%$ in both cases. Our results are limited by uncertainties in the geometry of the cluster gas, contamination from kinetic SZ ($\sim 10\%$), and the absolute calibration of the tSZ map ($7\%$). Investigation using a larger sample of clusters would help minimise these effects.

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arXiv2017

The XXL survey: first results and future

The XXL survey currently covers two 25 sq. deg. patches with XMM observations of ~10ks. We summarise the scientific results associated with the first release of the XXL data set, that occurred mid 2016. We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z<2) cluster, (z<4) AGN and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-$λ$ observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z>1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions.

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arXiv2016

Mapping the kinetic Sunyaev-Zel'dovich effect toward MACS J0717.5+3745 with NIKA

Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics of mergers, through which large scale structures form in the Universe. Velocity estimates within the intracluster medium (ICM) can be obtained via the Sunyaev-Zel'dovich (SZ) effect, but its observation is challenging both in term of sensitivity requirement and control of systematic effects, including the removal of contaminants. In this paper we report resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple merger MACS J0717.5+3745 (z=0.55), using data obtained with the NIKA camera at the IRAM 30m telescope. Assuming that the SZ signal is the sum of a thermal (tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we extract for the first time a resolved map of the kSZ signal in a cluster. The kSZ signal is dominated by a dipolar structure that peaks at -5.1 and +3.4 sigma, corresponding to two subclusters moving respectively away and toward us and coincident with the cold dense X-ray core and a hot region undergoing a major merging event. We model the gas electron density and line-of-sight velocity of MACS J0717.5+3745 as four subclusters. Combining NIKA data with X-ray observations from XMM-Newton and Chandra, we fit this model to constrain the gas line-of-sight velocity of each component, and we also derive, for the first time, a velocity map from kSZ data (i.e. that is model-dependent). Our results are consistent with previous constraints on the merger velocities, and thanks to the high angular resolution of our data, we are able to resolve the structure of the gas velocity. Finally, we investigate possible contamination and systematic effects with a special care given to radio and submillimeter galaxies. Among the sources that we detect with NIKA, we find one which is likely to be a high redshift lensed submillimeter galaxy.

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arXiv2016

The XXL Survey: VI. The 1000 brightest X-ray point sources

X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of active galactic nuclei (AGN). The XXL Survey spans two fields of a combined 50 $deg^2$ observed for more than 6Ms with XMM-Newton, occupying the parameter space between deep surveys and very wide area surveys; at the same time it benefits from a wealth of ancillary data. This paper marks the first release of the XXL point source catalogue selected in the 2-10 keV energy band with limiting flux $F_{2-10keV}=4.8\cdot10^{-14}\rm{erg\,s^{-1}\,cm^{-2}}$. We use both public and proprietary data sets to identify the counterparts of the X-ray point-like sources and improved upon the photometric redshift determination for AGN by applying a Random Forest classification trained to identify for each object the optimal photometric redshift model library. We also assign a probability to each source to be a star or an outlier. We model with Bayesian analysis the X-ray spectra assuming a power-law model with the presence of an absorbing medium. We find an average unabsorbed photon index of $Γ=1.85$ and average hydrogen column density $\log{N_{H}}=21.07 cm^{-2}$. We find no trend of $Γ$ or $N_H$ with redshift and a fraction of 26% absorbed sources ($\log N_{H}>22$). We show that the XXL-1000-AGN number counts extended the number counts of the COSMOS survey to higher fluxes and are fully consistent with the Euclidean expectation. We constrain the intrinsic luminosity function of AGN in the 2-10 keV energy band where the unabsorbed X-ray flux is estimated from the X-ray spectral fit up to z=3. Finally, we demonstrate the presence of a supercluster size structure at redshift 0.14, identified by means of percolation analysis of the XXL-1000-AGN sample. The XXL survey, reaching a medium flux limit and covering a wide area is a stepping stone between current deep fields and planned wide area surveys.

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arXiv2016

The XXL Survey VIII: MUSE characterisation of intracluster light in a z$\sim$0.53 cluster of galaxies

Within a cluster, gravitational effects can lead to the removal of stars from their parent galaxies. Gas hydrodynamical effects can additionally strip gas and dust from galaxies. The properties of the ICL can therefore help constrain the physical processes at work in clusters by serving as a fossil record of the interaction history. The present study is designed to characterise this ICL in a ~10^14 M_odot and z~0.53 cluster of galaxies from imaging and spectroscopic points of view. By applying a wavelet-based method to CFHT Megacam and WIRCAM images, we detect significant quantities of diffuse light. These sources were then spectroscopically characterised with MUSE. MUSE data were also used to compute redshifts of 24 cluster galaxies and search for cluster substructures. An atypically large amount of ICL has been detected in this cluster. Part of the detected diffuse light has a very weak optical stellar component and apparently consists mainly of gas emission, while other diffuse light sources are clearly dominated by old stars. Furthermore, emission lines were detected in several places of diffuse light. Our spectral analysis shows that this emission likely originates from low-excitation parameter gas. The stellar contribution to the ICL is about 2.3x10^9 yrs old even though the ICL is not currently forming a large number of stars. On the other hand, the contribution of the gas emission to the ICL in the optical is much greater than the stellar contribution in some regions, but the gas density is likely too low to form stars. These observations favour ram pressure stripping, turbulent viscous stripping, or supernovae winds as the origin of the large amount of intracluster light. Since the cluster appears not to be in a major merging phase, we conclude that ram pressure stripping is the most plausible process that generates the observed ICL sources.

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arXiv2015

The XXL Survey: I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme

We present the XXL Survey, the largest XMM programme totaling some 6.9 Ms to date and involving an international consortium of roughly 100 members. The XXL Survey covers two extragalactic areas of 25 deg2 each at a point-source sensitivity of ~ 5E-15 erg/sec/cm2 in the [0.5-2] keV band (completeness limit). The survey's main goals are to provide constraints on the dark energy equation of state from the space-time distribution of clusters of galaxies and to serve as a pathfinder for future, wide-area X-ray missions. We review science objectives, including cluster studies, AGN evolution, and large-scale structure, that are being conducted with the support of approximately 30 follow-up programmes. We describe the 542 XMM observations along with the associated multi-lambda and numerical simulation programmes. We give a detailed account of the X-ray processing steps and describe innovative tools being developed for the cosmological analysis. The paper provides a thorough evaluation of the X-ray data, including quality controls, photon statistics, exposure and background maps, and sky coverage. Source catalogue construction and multi-lambda associations are briefly described. This material will be the basis for the calculation of the cluster and AGN selection functions, critical elements of the cosmological and science analyses. The XXL multi-lambda data set will have a unique lasting legacy value for cosmological and extragalactic studies and will serve as a calibration resource for future dark energy studies with clusters and other X-ray selected sources. With the present article, we release the XMM XXL photon and smoothed images along with the corresponding exposure maps. The XMM XXL observation list (Table B.1) is available in electronic form at the CDS. The present paper is the first in a series reporting results of the XXL-XMM survey.

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arXiv2015

The XXL Survey. II. The bright cluster sample: catalogue and luminosity function

Context. The XXL Survey is the largest survey carried out by the XMM-Newton satellite and covers a total area of 50 square degrees distributed over two fields. It primarily aims at investigating the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. Aims. This article presents the XXL bright cluster sample, a subsample of 100 galaxy clusters selected from the full XXL catalogue by setting a lower limit of $3\times 10^{-14}\,\mathrm{erg \,s^{-1}cm^{-2}}$ on the source flux within a 1$^{\prime}$ aperture. Methods. The selection function was estimated using a mixture of Monte Carlo simulations and analytical recipes that closely reproduce the source selection process. An extensive spectroscopic follow-up provided redshifts for 97 of the 100 clusters. We derived accurate X-ray parameters for all the sources. Scaling relations were self-consistently derived from the same sample in other publications of the series. On this basis, we study the number density, luminosity function, and spatial distribution of the sample. Results. The bright cluster sample consists of systems with masses between $M_{500}=7\times 10^{13}$ and $3\times 10^{14} M_\odot$, mostly located between $z=0.1$ and 0.5. The observed sky density of clusters is slightly below the predictions from the WMAP9 model, and significantly below the predictions from the Planck 2015 cosmology. In general, within the current uncertainties of the cluster mass calibration, models with higher values of $σ_8$ and/or $Ω_m$ appear more difficult to accommodate. We provide tight constraints on the cluster differential luminosity function and find no hint of evolution out to $z\sim1$. We also find strong evidence for the presence of large-scale structures in the XXL bright cluster sample and identify five new superclusters.

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arXiv2015

The XXL Survey VII: A supercluster of galaxies at z=0.43

The XXL Survey is the largest homogeneous and contiguous survey carried out with XMM-Newton. Covering an area of 50 square degrees distributed over two fields, it primarily investigates the large-scale structures of the Universe using the distribution of galaxy clusters and active galactic nuclei as tracers of the matter distribution. Given its depth and sky coverage, XXL is particularly suited to systematically unveiling the clustering of X-ray clusters and to identifying superstructures in a homogeneous X-ray sample down to the typical mass scale of a local massive cluster. A friends-of-friends algorithm in three-dimensional physical space was run to identify large-scale structures. In this paper we report the discovery of the highest redshift supercluster of galaxies found in the XXL Survey. We describe the X-ray properties of the clusters members of the structure and the optical follow-up. The newly discovered supercluster is composed of six clusters of galaxies at a median redshift z around 0.43 and distributed across approximately 30 by 15 arc minutes (10 by 5 Mpc on sky) on the sky. This structure is very compact with all the clusters residing in one XMM pointing; for this reason this is the first supercluster discovered with the XXL Survey. Spectroscopic follow-up with WHT (William Herschel Telescope) and NTT (New Technology Telescope) confirmed a median redshift of z = 0.43. An estimate of the X-ray mass and luminosity of this supercluster and of its total gas mass put XLSSC-e at the average mass range of superclusters; its appearance, with two members of equal size, is quite unusual with respect to other superclusters and provides a unique view of the formation process of a massive structure.

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arXiv2015

Next Generation Cosmology: Constraints from the Euclid Galaxy Cluster Survey

We study the characteristics of the galaxy cluster samples expected from the European Space Agency's Euclid satellite and forecast constraints on cosmological parameters describing a variety of cosmological models. The method used in this paper, based on the Fisher Matrix approach, is the same one used to provide the constraints presented in the Euclid Red Book (Laureijs et al.2011). We describe the analytical approach to compute the selection function of the photometric and spectroscopic cluster surveys. Based on the photometric selection function, we forecast the constraints on a number of cosmological parameter sets corresponding to different extensions of the standard LambdaCDM model. The dynamical evolution of dark energy will be constrained to Delta w_0=0.03 and Delta w_a=0.2 with free curvature Omega_k, resulting in a (w_0,w_a) Figure of Merit (FoM) of 291. Including the Planck CMB covariance matrix improves the constraints to Delta w_0=0.02, Delta w_a=0.07 and a FoM=802. The amplitude of primordial non-Gaussianity, parametrised by f_NL, will be constrained to Δf_NL ~ 6.6 for the local shape scenario, from Euclid clusters alone. Using only Euclid clusters, the growth factor parameter γ, which signals deviations from GR, will be constrained to Delta γ=0.02, and the neutrino density parameter to Delta Omega_ν=0.0013 (or Delta \sum m_ν=0.01). We emphasise that knowledge of the observable--mass scaling relation will be crucial to constrain cosmological parameters from a cluster catalogue. The Euclid mission will have a clear advantage in this respect, thanks to its imaging and spectroscopic capabilities that will enable internal mass calibration from weak lensing and the dynamics of cluster galaxies. This information will be further complemented by wide-area multi-wavelength external cluster surveys that will already be available when Euclid flies. [Abridged]

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arXiv2014

The XMM-LSS survey: the Class 1 cluster sample over the extended 11 deg$^2$ and its spatial distribution

This paper presents 52 X-ray bright galaxy clusters selected within the 11 deg$^2$ XMM-LSS survey. 51 of them have spectroscopic redshifts ($0.05 3 σ$) constraints on the presence of a large void in the cluster distribution. We work out alternative hypotheses and demonstrate that a negative redshift evolution in the normalization of the $L_{X}-T_X$ relation (with respect to a self-similar evolution) is a plausible explanation for the observed deficit. We confirm this evolutionary trend by directly studying how C1 clusters populate the $L_{X}-T_X-z$ space, properly accounting for selection biases. We point out that a systematically evolving, unresolved, central component in clusters and groups (AGN contamination or cool core) can impact the classification as extended sources and be partly responsible for the observed redshift distribution.[abridged]

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arXiv2014

The mass profile and dynamical status of the z~0.8 galaxy cluster LCDCS 0504

Constraints on the mass distribution in high-redshift clusters of galaxies are not currently very strong. We aim to constrain the mass profile, M(r), and dynamical status of the $z \sim 0.8$ LCDCS 0504 cluster of galaxies characterized by prominent giant gravitational arcs near its center. Our analysis is based on deep X-ray, optical, and infrared imaging, as well as optical spectroscopy. We model the mass distribution of the cluster with three different mass density profiles, whose parameters are constrained by the strong lensing features of the inner cluster region, by the X-ray emission from the intra-cluster medium, and by the kinematics of 71 cluster members. We obtain consistent M(r) determinations from three methods (dispersion-kurtosis, caustics and MAMPOSSt), out to the cluster virial radius and beyond. The mass profile inferred by the strong lensing analysis in the central cluster region is slightly above, but still consistent with, the kinematics estimate. On the other hand, the X-ray based M(r) is significantly below both the kinematics and strong lensing estimates. Theoretical predictions from $Λ$CDM cosmology for the concentration--mass relation are in agreement with our observational results, when taking into account the uncertainties in both the observational and theoretical estimates. There appears to be a central deficit in the intra-cluster gas mass fraction compared to nearby clusters. Despite the relaxed appearance of this cluster, the determinations of its mass profile by different probes show substantial discrepancies, the origin of which remains to be determined. The extension of a similar dynamical analysis to other clusters of the DAFT/FADA survey will allow to shed light on the possible systematics that affect the determination of mass profiles of high-z clusters, possibly related to our incomplete understanding of intracluster baryon physics.

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arXiv2012

Distant galaxy clusters in the XMM Large Scale Structure survey

(Abridged) Distant galaxy clusters provide important tests of the growth of large scale structure in addition to highlighting the process of galaxy evolution in a consistently defined environment at large look back time. We present a sample of 22 distant (z>0.8) galaxy clusters and cluster candidates selected from the 9 deg2 footprint of the overlapping X-ray Multi Mirror (XMM) Large Scale Structure (LSS), CFHTLS Wide and Spitzer SWIRE surveys. Clusters are selected as extended X-ray sources with an accompanying overdensity of galaxies displaying optical to mid-infrared photometry consistent with z>0.8. Nine clusters have confirmed spectroscopic redshifts in the interval 0.8 0.8 clusters.

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arXiv2011

Galaxy cluster searches based on photometric redshifts in the four CFHTLS Wide fields

We have developed a method for detecting clusters in large imaging surveys, based on the detection of structures in galaxy density maps made in slices of photometric redshifts. This method was first applied to the Canada France Hawaii Telescope Legacy Survey (CFHTLS) Deep 1 field by Mazure et al. (2007), then to all the Deep and Wide CFHTLS fields available in the T0004 data release by Adami et al. (2010). The validity of the cluster detection rate was estimated by applying the same procedure to galaxies from the Millennium simulation. Here we analyse with the same method the full CFHTLS Wide survey, based on the T0006 data release. In a total area of 154 deg2, we have detected 4061 candidate clusters at 3sigma or above (6802 at 2sigma and above), in the redshift range 0.1<=z<=1.15, with estimated mean masses between 1.3 10^14 and 12.6 10^14 M_solar. This catalogue of candidate clusters will be available online via VizieR. We compare our detections with those made in various CFHTLS analyses with other methods. By stacking a subsample of clusters, we show that this subsample has typical cluster characteristics (colour-magnitude relation, galaxy luminosity function). We also confirm that the cluster-cluster correlation function is comparable to that obtained for other cluster surveys and analyze large scale filamentary galaxy distributions. We have increased the number of known optical high redshift cluster candidates by a large factor, an important step towards obtaining reliable cluster counts to measure cosmological parameters. The clusters that we detect behave as expected for a sample of clusters fed by filaments at the intersection of which they are located.

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