Ben J Maughan

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

Context. The quest for the cosmological parameters that describe our universe continues to motivate the scientific community to undertake very large survey initiatives across the electromagnetic spectrum. Over the past two decades, the Chandra and XMM-Newton observatories have supported numerous studies of X-ray-selected clusters of galaxies, active galactic nuclei (AGNs), and the X-ray background. The present paper is the first in a series reporting results of the XXL-XMM survey; it comes at a time when the Planck mission results are being finalised. Aims. 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 deg(2) each at a point-source sensitivity of similar to 5 x 10(-15) erg s(-1) cm(-2) in the [0.5-2] keV band (completeness limit). The surveys 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. Methods. 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. Results. 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. Conclusions. 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.

SUNYAEV-ZEL'DOVICH-MEASURED PRESSURE PROFILES FROM THE BOLOCAM X-RAY/SZ GALAXY CLUSTER SAMPLE

We describe Sunyaev-Zel’dovich (SZ) effect measurements and analysis of the intracluster medium (ICM) pressure profiles of a set of 45 massive galaxy clusters imaged using Bolocam at the Caltech Submillimeter Observatory. We deproject the average pressure profile of our sample into 13 logarithmically spaced radial bins between 0.07R500 and 3.5R500, and we find that a generalized Navarro, Frenk, and White (gNFW) profile describes our data with sufficient goodness-of-fit and best-fit parameters (C500, �, �, , P0 = 1.18, 0.86, 3.67, 0.67, 4.29). We use X-ray data to define cool-core and disturbed subsamples of clusters, and we constrain the average pressure profiles of each of these subsamples. We find that, given the precision of our data, the average pressure profiles of disturbed and cool-core clusters are consistent with one another at R & 0.15R500, with cool-core systems showing indications of higher pressure at R . 0.15R500. In addition, for the first time, we place simultaneous constraints on the mass scaling of cluster pressure profiles, their ensemble mean profile, and their radius-dependent intrinsic scatter between 0.1R500 and 2.0R500. The scatter among profiles is minimized at radii between ≃ 0.2R500 and ≃ 0.5R500, with a value of ≃ 20%. These results for the intrinsic scatter are largely consistent with previous analyses, most of which have relied heavily on X-ray derived pressures of clusters at significantly lower masses and redshifts compared to our sample. Therefore, our data provide further evidence that cluster pressure profiles are largely universal with scatter of ≃ 20–40% about the universal profile over a wide range of masses and redshifts. Subject headings: galaxies: clusters: general — galaxies: clusters: intracluster medium

Chandra X-ray analysis of the massive high-redshift galaxy clusters Cl J1113.1-2615 and Cl J0152.7-1357

We present an analysis of Chandra observations of two high-redshift clusters of galaxies, Cl J1113.1-2615 at z = 0.725 and Cl J0152.7-1357 at z = 0.833. We find Cl J1113.1-2615 to be morphologically relaxed with a temperature of kT = 4.3 keV and a mass (within the virial radius) of 4.3 ? 1014 M?. Cl J0152.7-1357, by contrast, is resolved into a northern and southern subcluster, each massive and X-ray-luminous, in the process of merging. The temperatures of the subclusters are found to be 5.5 and 5.2 keV, respectively, and we estimate their respective masses to be 6.1 ? 1014 and 5.2 ? 1014 M? within the virial radii. A dynamical analysis of the system shows that the subclusters are likely to be gravitationally bound. If the subclusters merge, they will form a system with a mass similar to that of the Coma Cluster. Two-dimensional modeling of the X-ray surface brightness reveals excess emission between the subclusters, suggestive, but not conclusive, evidence of a shock front. We make a first attempt at measuring the cluster M-T relation at z ? 0.8 and find no evolution in its normalization, supporting the previous assumption of an unevolving M-T relation when constraining cosmological parameters from cluster evolution studies. A comparison of the cluster properties with those of nearby systems also finds little or no evolution in the L-T relation, the gas fraction-T relation, the ?-T relation, or the metallicity. These results suggest that, in at least some massive clusters, the hot gas was in place, and containing its metals, at z ? 0.8 and thus that the clusters were assembled at redshifts significantly higher than z = 0.8, as predicted in low-?M models. We also highlight the need to correct for the degradation of the Chandra ACIS low-energy quantum efficiency in high-redshift cluster studies when the low-energy absorption is often assumed to be the Galactic value, rather than measured.

JKCS 041: a colour-detected galaxy cluster at zphot ∼ 1.9 with deep potential well as confirmed by X-ray data

We report the discovery of JKCS 041, a massive near-infrared selected cluster of galaxies at zphot ∼ 1.9. The cluster was originally discovered using a modified red-sequence method and also detected in follow-up Chandra data as an extended X-ray source. Optical and near-infrared imaging data alone allow us to show that the detection of JKCS 041 is secure, even in the absence of the X-ray data. We investigate the possibility that JKCS 041 is not a galaxy cluster at z ∼ 1.9, and find other explanations unlikely. The X-ray detection and statistical arguments rule out the hypothesis that JKCS 041 is actually a blend of groups along the line of sight, and we find that the X-ray emitting gas is too hot and dense to be a filament projected along the line of sight. The absence of a central radio source and the extent and morphology of the X-ray emission argue against the possibility that the X-ray emission comes from inverse Compton scattering of CMB photons by a radio plasma. The cluster has an X-ray core radius of 36.6 +8.3 −7.6 arcsec (about 300 kpc), an X-ray temperature of 7.4 +5.3 −3.3 keV, a bolometric X-ray luminosity within R500 of (7.6 ± 0.5) × 10 44 erg s −1 , and an estimated mass of M500 = 2.9 +3.8 −2.4 × 10 14 M � , the last derived under the usual (and strong) assumptions. The cluster is composed of 16.4 ± 6.3 galaxies within 1.5 arcmin (750 kpc) brighter than K ∼ 20.7 mag. The high redshift of JKCS 041 is determined from the detection colour, from the detection of the cluster in a galaxy sample formed by zphot > 1.6 galaxies and from a photometric redshift based on 11-band spectral energy distribution fitting. By means of the latter we find the cluster redshift to be 1.84 < z < 2.12 at 68% confidence. Therefore, JKCS 041 is a cluster of galaxies at zphot ∼ 1.9 with a deep potential well, making it the most distant cluster with extended X-ray emission known.

Baryon Content of Massive Galaxy Clusters at z = 0-0.6

We study the relationship between two major baryonic components in galaxy clusters, namely the stars in galaxies and the ionized gas in the intracluster medium (ICM), using 94 clusters that span the redshift range 0-0.6. Accurately measured total and ICM masses from Chandra observations and stellar masses derived from the Wide-field Infrared Survey Explorer and the Two Micron All Sky Survey allow us to trace the evolution of cluster baryon content in a self-consistent fashion. We find that, within r 500, the evolution of the ICM-mass-total-mass relation is consistent with the expectation of the self-similar model, while there is no evidence for redshift evolution in the stellar-mass-total-mass relation. This suggests that the stellar mass and ICM mass in the inner parts of clusters evolve differently.

An XMM–Newton observation of the massive, relaxed galaxy cluster ClJ1226.9+3332 at z= 0.89

A detailed X-ray analysis of an XMM-Newton observation of the high-redshift (z = 0.89) galaxy cluster ClJ1226.9+3332 is presented. After careful consideration of background subtraction issues, the X-ray temperature is found to be 11.5 +1.1 -0.9 keV, the highest X-ray temperature of any cluster at z > 0.6. The temperature is consistent with the observed velocity dispersion. In contrast to MS 1054-0321, the only other very hot cluster currently known at z > 0.8, ClJ1226.9+3332, features a relaxed X-ray morphology, and its high overall gas temperature is not caused by one or several hotspots. The system thus constitutes a unique example of a high-redshift (z >0.8), high-temperature (T > 10 keV), relaxed cluster, for which the usual hydrostatic equilibrium assumption and the X-ray mass are most reliable. A temperature profile is constructed (for the first time at this redshift) and is consistent with the cluster being isothermal out to 45 per cent of the virial radius. Within the virial radius (corresponding to a measured overdensity of a factor of 200), a total mass of 1.4 ± 0.5 x 10 15 M ○. is derived, with a gas mass fraction of 12 ± 5 per cent (for a A cold dark matter cosmology and H 0 = 70 km s -1 Mpc -1 ). This total mass is similar to that of the Coma cluster. The bolometric X-ray luminosity is 5.3 +0.2 -0.2 x 10 45 erg s -1 . Analysis of a short Chandra observation confirms the lack of significant point-source contamination, the temperature, and the luminosity, albeit with lower precision. The probabilities of finding a cluster of this mass within the volume of the discovery X-ray survey are ∼8 x 10 -5 for Ω M = 1 and 0.64 for Ω M = 0.3, making Ω M = 1 highly unlikely. The entropy profile suggests that entropy evolution is being observed. The metal abundance (of Z = 0.33 +0.14 -0.10 Z ○. ), gas mass fraction and gas distribution are consistent with those of local clusters; thus the bulk of the metals were in place by z = 0.89.

A comprehensive picture of baryons in groups and clusters of galaxies

(Abridged) Based on XMM-Newton, Chandra and SDSS data, we investigate the baryon distribution in groups and clusters and its use as a cosmological constraint. For this, we considered a sample of 123 systems, with total masses in the mass range M500 = ~ 10^13 - 4 x 10^15 h_70^-1 Msun. The gas masses and total masses are derived from X-ray data under the assumption of hydrostatic equilibrium and spherical symmetry. The stellar masses are based on SDSS-DR8 data. For the 37 systems out of 123 that had both optical and X-ray data available, we investigated the gas, stellar and total baryon mass fractions inside r2500 and r500, and the differential gas mass fraction within the spherical annulus between r2500 and r500, as a function of total mass. For the other objects, we investigated the gas mass fraction only. We find that the gas mass fraction inside r2500 and r500 depends on the total mass. However, the differential gas mass fraction does not show any dependence on total mass for systems with M500 > 10^14 Msun. We find that the total baryonic content increases with cluster mass. This led us to investigate the contribution of the ICL to the total baryon budget for lower mass systems, but we find that it cannot account for the difference observed. The gas mass fraction dependence on total mass observed for groups and clusters could be due to the difficulty of low-mass systems to retain gas inside the inner region. Due to their shallower potential well, non-thermal processes are more effective in expelling the gas from their central regions outwards. Since the differential gas mass fraction is nearly constant it provides better constraints for cosmology. Using our total f_b estimates, our results imply 0.17 < Omega_m < 0.55.

Chandra X-ray observations of Abell 1835 to the virial radius

We report the first Chandra detection of emission out to the virial radius in the cluster Abell 1835 at z = 0.253. Our analysis of the soft X-ray surface brightness shows that emission is present out to a radial distance of 10 arcmin or 2.4 Mpc, and the temperature profile has a factor of ten drop from the peak temperature of 10 keV to the value at the virial radius. We model the Chandra data from the core to the virial radius and show that the steep temperature profile is not compatible with hydrostatic equilibrium of the hot gas, and that the gas is convectively unstable at the outskirts. A possible interpretation of the Chandra data is the presence of a second phase of warm-hot gas near the cluster’s virial radius that is not in hydrostatic equilibrium with the cluster’s potential. The observations are also consistent with an alternative scenario in which the gas is significantly clumped at large radii.

Chandra measurements of a complete sample of X-ray luminous galaxy clusters: the gas mass fraction

We present Chandra X-ray measurements of the gas mass fraction out to r500 for a complete sample of the 35 most luminous clusters from the Brightest Cluster Sample and the Extended Brightest Cluster Sample at redshift z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data were analysed independently using two pipelines and two different models for the gas density and temperature. We measure an average of fgas(r500) = 0.163 +/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b / Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar baryon fraction. Earlier studies reported gas mass fractions significantly lower than the cosmic baryon fraction at r500, and in some cases higher values that are consistent with the cosmic baryon fraction towards the virial radius.In this paper we show that the most X-ray luminous clusters in the redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the cosmic value at r500.

The XXL Survey III. Luminosity-temperature relation of the bright cluster sample

Context. The XXL Survey is the largest homogeneous survey carried out with XMM-Newton. Covering an area of 50 deg(2), the survey contains several hundred galaxy clusters out to a redshift of similar to 2 above an X-ray flux limit of similar to 5 x 10(-15) erg cm(-2) s(-1). This paper belongs to the first series of XXL papers focusing on the bright cluster sample. Aims. We investigate the luminosity-temperature (LT) relation for the brightest clusters detected in the XXL Survey, taking fully into account the selection biases. We investigate the form of the LT relation, placing constraints on its evolution. Methods. We have classified the 100 brightest clusters in the XXL Survey based on their measured X- ray flux. These 100 clusters have been analysed to determine their luminosity and temperature to evaluate the LT relation. We used three methods to fit the form of the LT relation, with two of these methods providing a prescription to fully take into account the selection effects of the survey. We measure the evolution of the LT relation internally using the broad redshift range of the sample. Results. Taking fully into account selection effects, we find a slope of the bolometric LT relation of B-LT = 3.08 +/- 0.15, steeper than the self-similar expectation (B-LT = 2). Our best- fit result for the evolution factor is E(z)(1.64 +/- 0.77), fully consistent with “strong self-similar” evolution where clusters scale self- similarly with both mass and redshift. However, this result is marginally stronger than “weak self-similar” evolution, where clusters scale with redshift alone. We investigate the sensitivity of our results to the assumptions made in our fitting model, finding that using an external LT relation as a low-z baseline can have a profound effect on the measured evolution. However, more clusters are needed in order to break the degeneracy between the choice of likelihood model and mass-temperature relation on the derived evolution.