F. Pacaud

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.

eROSITA on SRG

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian/German Spektrum-Roentgen-Gamma (SRG) mission which is now officially scheduled for launch on March 26, 2016. eROSITA will perform a deep survey of the entire X-ray sky. In the soft band (0.5-2 keV), it will be about 30 times more sensitive than ROSAT, while in the hard band (2-8 keV) it will provide the first ever true imaging survey of the sky. The design driving science is the detection of large samples of galaxy clusters to redshifts z < 1 in order to study the large scale structure in the universe and test cosmological models including Dark Energy. In addition, eROSITA is expected to yield a sample of a few million AGN, including obscured objects, revolutionizing our view of the evolution of supermassive black holes. The survey will also provide new insights into a wide range of astrophysical phenomena, including X-ray binaries, active stars and diffuse emission within the Galaxy. eROSITA is currently (June 2014) in its flight model and calibration phase. All seven flight mirror modules (+ 1 spare) have been delivered and measured in X-rays. The first camera including the complete electronics has been extensively tested (vacuum + X-rays). A pre-test of the final end-toend test has been performed already. So far, all subsystems and components are well within their expected performances.

Precision cosmology with a wide area XMM cluster survey

We explore the cosmological constraints expected from wide area XMM-type cluster surveys covering 50–200 deg2, under realistic observing conditions. We perform a Fisher matrix analysis, based on cluster number counts in combination with estimates of the two-point cluster correlation function. The effect of the survey design is implemented through an observationally well-tested cluster selection function. Special attention is given to the modelling of the shot noise and sample variance, which we estimate by applying our selection function to numerically simulated surveys. We then infer the constraints on the equation of state of the dark energy, considering various survey configurations. We quantitatively investigate the respective impact of the cluster mass measurements, of the correlation function and of the 1 < z < 2 cluster population. We show that, with some 20 Ms XMM observing time, it is possible to constrain the dark energy parameters at a level comparable to that expected from the next generation of cosmic probes. Such a survey also has the power to provide unique insights into the physics of high-redshift clusters and the properties of active galactic nuclei.

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 cosmological analysis of X-ray cluster surveys – II. Application of the CR–HR method to the XMM archive

We have processed 2774 high galactic observations from the XMM archive (as of 2010 May) and extracted a serendipitous catalogue of some 850 clusters of galaxies based on purely X-ray criteria, following the methodology developed for the XMM-Large-Scale Survey. Restricting the sample to the highest signal-to-noise ratio objects (347 clusters), we perform a cosmological analysis using only the X-ray information. The analysis consists in the modelling of the observed colour–magnitude [count rate and hardness ratio (CR–HR)] diagram constructed from cluster instrumental count rates measured in the [0.5–2], [1–2] and [0.5–1] keV bands. A Monte Carlo Markov chain procedure simultaneously fits the cosmological parameters, the evolution of the cluster scaling laws and the selection effects. Our results are consistent with the σ8 and Ωm values obtained by the 5-year Wilkinson Microwave Anisotropy Probe (WMAP5) and point towards a negative evolution of the cluster scaling relations with respect to the self-similar expectation. We are further able to constrain the cluster fractional radius xc,0=rc/R500c to xc, 0= 0.24 ± 0.04. This study stresses again the critical role of selection effects in deriving cluster scaling relations, even in the local universe. Finally, we show that the CR–HR method applied to the eRosita all-sky survey – provided that cluster photometric redshifts are available – will enable the determination of the equation of state of the dark energy at the level of the Dark Energy Task Force (DETF) stage IV predictions; simultaneously, the evolution of the cluster scaling relations will be unambiguously determined. The XMM CLuster Archive Super Survey (X-CLASS) serendipitous cluster catalogue is available online at http://xmm-lss.in2p3.fr:8080/l4sdb/.

The XMM large scale structure survey: optical vs. X-ray classifications of active galactic nuclei and the unified scheme

Aims.Our goal is to characterize AGN populations by comparing their X-ray and optical classifications within the framework of the standard orientation-based unified scheme. Methods: We present a sample of 99 spectroscopically identified (R ? 22 mag) X-ray selected point sources in the XMM-LSS survey which are significantly detected (?3?) in the [ 2-10] keV band with fluxes between 8 × 10-15 and 8 × 10-14 erg s-1 cm-2, and which have more than 80 counts. We have compared their X-ray and optical classifications. To this end, we performed an X-ray spectral analysis for all of these 99 X-ray sources in order to assess whether they are intrinsically absorbed or not. The X-ray classification is based on the measured intrinsic column density. The optical classification is based on the measured FWHM of the permitted emission lines, the absence of broad lines being due to obscuration within the framework of the standard AGN unified scheme. Results: Introducing the fourfold point correlation coefficient r, we find a mild correlation between the X-ray and the optical classifications (r = 0.28), as up to 32 X-ray sources out of 99 have differing X-ray and optical classifications: on one hand, 10% of the type 1 sources (7/32) present broad emission lines in their optical spectra and strong absorption (N{H}int ? 1022 cm-2) in the X-rays. These objects are highly luminous AGN lying at high redshift and thus dilution effects by the host galaxy light are totally ruled out, their discrepant nature being an intrinsic property instead. Their X-ray luminosities and redshifts distributions are consistent with those of the unabsorbed X-ray sources with broad emission lines (L{2-10} 4 × 1044 erg s-1; z 1.9). On the other hand, 25/32 are moderate luminosity (L{2-10} ? 5 × 1043 erg s-1) AGN, which are both unabsorbed in the X-rays and only present narrow emission lines in their optical spectra. Based on their line ratios in the optical, the majority of them have an optical spectrum which is more representative of the host galaxy rather than of a reddened AGN. We finally infer that dilution of the AGN by the host galaxy seems to account for their nature. 5/25 have been defined as Seyfert 2 based on their optical spectra. In conclusion, most of these 32 discrepant cases can be accounted for by the standard AGN unified scheme, as its predictions are not met for only 12% of the 99 X-ray sources. Table 4 and Figs. [see full text]-[see full text] are only available in electronic form at http://www.aanda.org

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.

The Spitzer South Pole Telescope Deep Field: Survey Design and Infrared Array Camera Catalogs

The Spitzer South Pole Telescope Deep Field (SSDF) is a wide-area survey using Spitzers Infrared Array Camera (IRAC) to cover 94 deg^2 of extragalactic sky, making it the largest IRAC survey completed to date outside the Milky Way midplane. The SSDF is centered at (α, δ) = (23:30, –55:00), in a region that combines observations spanning a broad wavelength range from numerous facilities. These include millimeter imaging from the South Pole Telescope, far-infrared observations from Herschel/SPIRE, X-ray observations from the XMM XXL survey, near-infrared observations from the VISTA Hemisphere Survey, and radio-wavelength imaging from the Australia Telescope Compact Array, in a panchromatic project designed to address major outstanding questions surrounding galaxy clusters and the baryon budget. Here we describe the Spitzer/IRAC observations of the SSDF, including the survey design, observations, processing, source extraction, and publicly available data products. In particular, we present two band-merged catalogs, one for each of the two warm IRAC selection bands. They contain roughly 5.5 and 3.7 million distinct sources, the vast majority of which are galaxies, down to the SSDF 5σ sensitivity limits of 19.0 and 18.2 Vega mag (7.0 and 9.4 μJy) at 3.6 and 4.5 μm, respectively.

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.

The XXL Survey IV. Mass-temperature relation of the bright cluster sample

Context. The XXL Survey is the largest survey carried out by XMM-Newton. Covering an area of 50 deg(2), the survey contains similar to 450 galaxy clusters out to a redshift similar to 2 and to an X-ray flux limit of similar to 5 x 10(-1)5 erg s(-1) cm(-2). This paper is part of the first release of XXL results focussed on the bright cluster sample. Aims. We investigate the scaling relation between weak-lensing mass and X-ray temperature for the brightest clusters in XXL. The scaling relation discussed in this article is used to estimate the mass of all 100 clusters in XXL-100-GC. Methods. Based on a subsample of 38 objects that lie within the intersection of the northern XXL field and the publicly available CFHTLenS shear catalog, we derive the weak-lensing mass of each system with careful considerations of the systematics. The clusters lie at 0.1 \textless z \textless 0.6 and span a temperature range of T similar or equal to 1-5 keV. We combine our sample with an additional 58 clusters from the literature, increasing the range to T similar or equal to 1-10 keV. To date, this is the largest sample of clusters with weak-lensing mass measurements that has been used to study the mass-temperature relation. Results. The mass-temperature relation fit (M proportional to T-b) to the XXL clusters returns a slope b = 1.78(-0.32)(+0.37) and intrinsic scatter sigma(slnM\textbar T) similar or equal to 0.53; the scatter is dominated by disturbed clusters. The fit to the combined sample of 96 clusters is in tension with self-similarity, b = 1.67 +/- 0.12 and sigma(lnM vertical bar T) similar or equal to 0.41. Conclusions. Overall our results demonstrate the feasibility of ground-based weak-lensing scaling relation studies down to cool systems of similar to 1 keV temperature and highlight that the current data and samples are a limit to our statistical precision. As such we are unable to determine whether the validity of hydrostatic equilibrium is a function of halo mass. An enlarged sample of cool systems, deeper weak-lensing data, and robust modelling of the selection function will help to explore these issues further.