J. P. Willis

The XMM-LSS survey: the Class 1 cluster sample over the initial 5 deg2 and its cosmological modelling

We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the objects being groups with a temperature below 2 keV. Our L-T(z) relation points toward self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z=1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the L-T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10deg2 has the potential to exclude the non-evolution hypothesis, but that constraints on more refined ICM models will probably be limited by the large intrinsic dispersion of the L-T relation. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and T(M,z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass-flux and mass-count-rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming SZ surveys.

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

Limits on the luminosity function of Ly alpha emitters at z=7.7

Aims. The Ly alpha luminosity function (LF) of high-redshift Ly alpha emitters (LAEs) is one of the few observables of the re-ionization epoch accessible with 8-10 m class telescopes. The evolution of the LAE LF with redshift is dependent upon the physical evolution of LAEs and the ionisation state of the Universe towards the end of the Dark Ages. Methods. We performed a narrow-band imaging program at 1.06 mu m using CFHT/WIRCam. The observations target Lya emitters at redshift z similar to 7.7 in the CFHT-LS D1 field. From these observations we derived a photometric sample of 7 LAE candidates at z similar to 7.7. Results. We derive luminosity functions for the full sample of seven objects and for subsamples of four objects. Assuming the brightest objects in our sample are real, we find that the resulting luminosity function is not consistent with previous work at lower redshifts. More definitive conclusions will require spectroscopic confirmation.

A deep, narrow J-band search for protogalactic Lyα emission at redshifts z∼ 9

We present a deep, narrow J-band search for protogalactic Lya emission at redshifts z ∼ 9. We combine an exceptionally deep image of the Hubble Deep Field South, obtained using a narrow-band filter centred on the wavelength 1.187 μm using the VLT/ISAAC facility, with existing deep, broad-band images covering optical to near-infrared wavelengths. We search for z ∼ 9 Lya-emitting galaxies displaying a significant narrow-band excess relative to the J s band that are undetected at optical wavelengths. We detect no sources consistent with this criterion to the 90 per cent point-source flux limit of the narrow-band image, F NB = 3.28 x 10 -18 erg s -1 cm -2 . The survey selection function indicates that we have sampled a volume of approximately 340 h -3 Mpc 3 to a Lyα emission luminosity of 10 43 h -2 erg s -1 . We conclude by considering the potential implications for the physics of the high-redshift Universe.

The XMM-LSS survey: optical assessment and properties of different X-ray selected cluster classes

Context. XMM and Chandra opened a new area for the study of clusters of galaxies not only for cluster physics, but also for the detection of faint and distant clusters that were inaccessible with previous missions. Aims. This article presents 66 spectroscopically confirmed clusters (0.05 \textless= z \textless= 1.5) within an area of 6 deg(2) enclosed in the XMM-LSS survey. Almost two thirds have been confirmed with dedicated spectroscopy only and 10% have been confirmed with dedicated spectroscopy supplemented by literature redshifts. Methods. Sub-samples, or classes, of extended-sources are defined in a two-dimensional X-ray parameter space allowing for various degrees of completeness and contamination. We describe the procedure developed to assess the reality of these cluster candidates using the CFHTLS photometric data and spectroscopic information from our own follow-up campaigns. Results. Most of these objects are low-mass clusters, hence constituting a still poorly studied population. In a second step, we quantify the correlations between the optical properties such as richness or velocity dispersion and the cluster X-ray luminosities. We examine the relation of the clusters to the cosmic web. Finally, we review peculiar compact structures in the surveyed area such as very distant clusters and fossil groups.

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.

Evolution of the observed Lyα luminosity function from z = 6.5 to z = 7.7: evidence for the epoch of reionization?

Aims. Lyα emitters (LAEs) can be detected out to very high redshifts during the epoch of reionization. The evolution of the LAE luminosity function with redshift is a direct probe of the Lyα transmission of the intergalactic medium (IGM), and therefore of the IGM neutral-hydrogen fraction. Measuring the Lyα luminosity function (LF) of Lyα emitters at redshift z = 7.7 therefore allows us to constrain the ionizing state of the Universe at this redshift. Methods. We observed three 7. 5 × 7. 5 fields with the HAWK-I instrument at the VLT with a narrow band filter centred at 1.06 μm and targeting Lyα emitters at redshift z ∼ 7.7. The fields were chosen for the availability of multiwavelength data. One field is a galaxy cluster, the Bullet Cluster, which allowed us to use gravitational amplification to probe luminosities that are fainter than in the field. The two other fields are subareas of the GOODS Chandra Deep Field South and CFHTLS-D4 deep field. We selected z = 7.7 LAE candidates from a variety of colour criteria, in particular from the absence of detection in the optical bands. Results. We do not find any LAE candidates at z = 7.7 in ∼2.4 × 104 Mpc3 down to a narrow band AB magnitude of ∼26, which allows us to infer robust constraints on the Lyα LAE luminosity function at this redshift. Conclusions. The predicted mean number of objects at z = 6.5, derived from somewhat different luminosity functions of Hu et al. (2010, ApJ, 725, 394), Ouchi et al. (2010, ApJ, 723, 869), and Kashikawa et al. (2011, ApJ, 734, 119) are 2.5, 13.7, and 11.6, respectively. Depending on which of these luminosity functions we refer to, we exclude a scenario with no evolution from z = 6.5 to z = 7.7 at 85% confidence without requiring a strong change in the IGM Lyα transmission, or at 99% confidence with a significant quenching of the IGM Lyα transmission, possibly from a strong increase in the high neutral-hydrogen fraction between these two redshifts.

The discovery of two new galaxy—galaxy lenses from the Sloan Digital Sky Survey

The gravitational lens configuration where a background galaxy is closely aligned with a foreground galaxy, can provide accurate measurement of the dark matter density profile in the foreground galaxy, free of dynamical assumptions. Currently only three such galaxy-galaxy lenses are known where the lensed source has a confirmed redshift and is reasonably bright at optical wavelengths, and therefore suitable for observations with the HST Advanced Camera for Surveys (ACS). Two of these were discovered by noting an anomalous emission line (from the source) in the spectrum of a massive early-type galaxy (the lens). To find further galaxy-galaxy lenses suitable for ACS imaging we have looked for anomalous emission lines in the luminous red galaxy (LRG) subsample of the SDSS DR3 spectroscopic database. Our search methodology has similarities to that applied by Bolton et al. (which has had recent success), but extends the upper redshift limit for lensed sources to z=1.4. Here we report follow-up imaging and spectroscopic observations of two candidates, confirmed as gravitational lenses by the detection of multiple images in the line of [OII]3726,3729. In the first system, J145957.1-005522.8, the lens at z=0.58, consists of two LRGs. The anomalous emission line is confirmed as [OII] by the detection of the corresponding H-gamma line, providing a source redshift of z=0.94. In the second system, J230946.3-003912.9, the lens is a single LRG at z=0.29, and the source redshift is z=1.00, confirmed by partially resolving the [OII] doublet.

Combined analysis of weak lensing and X-ray blind surveys★

We present a joint weak lensing and X-ray analysis of 4 deg^2 from the CFHTLS and XMMLSS surveys. Our weak lensing analysis is the first analysis of a real survey using shapelets, a new generation weak lensing analysis method. We create projected mass maps of the images, and extract six weak-lensing-detected clusters of galaxies. We show that their counts can be used to constrain the power-spectrum normalization σ8 = 0.92^(+0.26)_(−0.30) for Ωm = 0.24. We show that despite the large scatter generally observed in the mass–temperature (M–T) relation derived from lensing masses, tight constraints on both its slope and normalization M∗ can be obtained with a moderate number of sources provided that the covered mass range is large enough. Adding clusters given by Bardeau et al. to our sample, we measure M∗ =2.71^(+0.79)_(−0.61) × 10^(14) h^(−1) Mסּ. Although they are dominated by shot noise and sample variance, our measurements are consistent with currently favoured values, and set the stage for future surveys. We thus investigate the dependence of those estimates on survey size, depth and integration time, for joint weak lensing and X-ray surveys. We show that deep surveys should be dedicated to the study of the physics of clusters and groups of galaxies. For a given exposure time, wide surveys provide a larger number of detected clusters and are therefore preferred for the measurement of cosmological parameters, such as σ8 and M∗.We show that a wide survey of a few hundred square degrees is needed to improve upon current measurements of these parameters. More ambitious surveys covering 7000 deg^2 will provide the 1 per cent accuracy in the estimation of the power-spectrum and the M–T relation normalizations.

The XMM Large-Scale Structure survey: a well-controlled X-ray cluster sample over the D1 CFHTLS area

We present the XMM Large-Scale Structure Survey (XMM-LSS) cluster catalogue corresponding to the Canada-France-Hawaii Telescope Legacy Survey Dl area. The list contains 13 spectroscopically confirmed, X-ray selected galaxy clusters over 0.8 deg 2 to a redshift of unity and so constitutes the highest density sample of clusters to date. Cluster X-ray bolometric luminosities range from 0.03 to 5 x 10 44 erg s -1 . In this study, we describe our catalogue construction procedure: from the detection of X-ray cluster candidates to the compilation of a spectroscopically confirmed cluster sample with an explicit selection function. The procedure further provides basic X-ray products such as cluster temperature, flux and luminosity. We detected slightly more clusters with (0.5-2.0 keV) X-ray fluxes of >2 x 10 -14 erg s -1 cm -2 than we expected based on expectations from deep ROSAT surveys. We also present the luminosity-temperature relation for our nine brightest objects possessing a reliable temperature determination. The slope is in good agreement with the local relation, yet compatible with a luminosity enhancement for the 0.15 < z < 0.35 objects having 1 < T < 2 keV, a population that the XMM-LSS is identifying systematically for the first time. The present study permits the compilation of cluster samples from XMM images whose selection biases are understood. This allows, in addition to studies of large-scale structure, the systematic investigation of cluster scaling law evolution, especially for low mass X-ray groups which constitute the bulk of our observed cluster population. All cluster ancillary data (images, profiles, spectra) are made available in electronic form via the XMM-LSS cluster data base.