We report the discovery of a massive, X-ray-luminous cluster of galaxies at z=1.393, the most distant X-ray-selected cluster found to date. XMMU J2235.3-2557 was serendipitously detected as an extended X-ray source in an archival XMM-Newton observation of NGC 7314. VLT-FORS2 R and z band snapshot imaging reveals an over-density of red galaxies in both angular and color spaces. The galaxy enhancement is coincident in the sky with the X-ray emission; the cluster red sequence at R − z ≃ 2.1 identifies it as a high-redshift candidate. Subsequent VLT-FORS2 multi-object spectroscopy unambiguously confirms the presence of a massive cluster based on 12 concordant redshifts in the interval 1.38 < z < 1.40. The preliminary cluster velocity dispersion is 762 ± 265 km s −1 . VLT-ISAAC Ks and J band images underscore the rich distribution of red galaxies associated with the cluster. Based on a 45 ks XMM-Newton observation, we find the cluster has an aperture-corrected, unabsorbed X-ray flux of f X = (3.6 ± 0.3) × 10 −14 ergs cm −2 s −1 , a rest-frame X-ray luminosity of L X = (3.0 ± 0.2) × 10 44 h −2 70 ergs s −1 (0.5-2.0 keV), and a temperature of kT = 6.0 +2.5 −1.8 keV. Though XMMU J2235.3-2557 is likely the first confirmed z > 1 cluster found with XMM-Newton, the relative ease and efficiency of discovery demonstrates that it should be possible to build large samples of z > 1 clusters through the joint use of X-ray and large, ground-based telescopes.

Context. A precise understanding of the relations between observable X-ray properties of galaxy clusters and cluster mass is a vital part of the application of X-ray galaxy cluster surveys to test cosmological models. An understanding of how these relations evolve with redshift is just emerging from a number of observational data sets. Aims. The current literature provides a diverse and inhomogeneous picture of scaling relation evolution. We attempt to transform these results and the data on recently discovered distant clusters into an updated and consistent framework, and provide an overall view of scaling relation evolution from the combined data sets. Methods. We study in particular the most important scaling relations connecting X-ray luminosity, temperature, and cluster mass (M-T , L X -T , and M-L X ) combining 14 published data sets supplemented with recently published data of distant clusters and new results from follow-up observations of the XMM-Newton Distant Cluster Project (XDCP) that adds new leverage to efficiently constrain the scaling relations at high redshift. Results. We find that the evolution of the mass-temperature relation is consistent with the self-similar evolution prediction, while the evolution of X-ray luminosity for a given temperature and mass for a given X-ray luminosity is slower than predicted by simple self-similar models. Our best fit results for the evolution factor E(z) α are α = −1.04 ± 0.07 for the M-T relation, α = −0.23−0.62 for the L-T relation, and α = −0.93−0.12 for the M-L X relation. We also explore the influence of selection effects on scaling relations and find that selection biases are the most likely reason for apparent inconsistencies between different published data sets. Conclusions. The new results provide the currently most robust calibration of high-redshift cluster mass estimates based on X-ray luminosity and temperature and help us to improve the prediction of the number of clusters to be found in future galaxy cluster X-ray surveys, such as eROSITA. The comparison of evolution results with hydrodynamical cosmological simulations suggests that early preheating of the intracluster medium (ICM) provides the most suitable scenario to explain the observed evolution.

Context. The galaxy cluster XMMU J2235.3−2557 (hereafter XMM2235), spectroscopically confirmed at z = 1.39, is one of the most distant X-ray selected galaxy clusters. It has been at the center of a multi-wavelength observing campaign with ground and space facilities. Aims. We characterize the galaxy populations of passive members, the thermodynamical properties and metal abundance of the hot gas, and the total mass of the system using imaging data with HST/ACS (i 775 and z 850 bands) and VLT/ISAAC (J and K S bands), extensive spectroscopic data obtained with VLT/FORS2, and deep (196 ks) Chandra observations. Methods. Chandra data allow temperature and metallicity to be measured with good accuracy and the X-ray surface brightness profile to be traced out to 1 (or 500 kpc), thus allowing the mass to be reliably estimated. Out of a total sample of 34 spectroscopically confirmed cluster members, we selected 16 passive galaxies (without detectable [OII]) within the central 2 (or 1 Mpc) with ACS coverage, and inferred star formation histories for subsamples of galaxies inside and outside the core by modeling their spectrophotometric data with spectral synthesis models. Results. Chandra data show a regular elongated morphology, closely resembling the distribution of core galaxies, with a significant cool core. We measure a global X-ray temperature of kT = 8.6 +1.3 −1.2 keV (68% confidence), which we find to be robust against several systematics involved in the X-ray spectral analysis. By detecting the rest frame 6.7 keV Iron K line in the Chandra spectrum, we measure a metallicity Z = 0.26 +0.20 −0.16 Z . In the likely hypothesis of hydrostatic equilibrium, we obtain a total mass of M tot (< 1 Mpc) = (5.9 ± 1.3) × 10 14 M . By modeling both the composite spectral energy distributions and spectra of the passive galaxies in and outside the core, we find a strong mean age radial gradient. Core galaxies, with stellar masses in excess of 10 11 M , appear to have formed at an earlier epoch with a relatively short star formation phase (z = 5−6), whereas passive galaxies outside the core show spectral signatures suggesting a prolonged star formation phase to redshifts as low as z ≈ 2. Conclusions. Overall, our analysis implies that XMM2235 is the hottest and most massive bona-fide cluster discovered to date at z > 1, with a baryonic content, both its galaxy population and intracluster gas, in a significantly advanced evolutionary stage at 1/3 of the current age of the Universe.

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We present the largest sample of spectroscopically confirmed X-ray luminous high-redshift galaxy clusters to date comprising 22 systems in the range 0.9 < z < ∼ 1.6 as part of the XMM-Newton Distant Cluster Project (XDCP). All systems were initially selected as extended X-ray sources over 76.1 deg 2 of non-contiguous deep archival XMM-Newton coverage, of which 49.4 deg 2 are part of the core survey with a quantifiable selection function and 17.7 deg 2 are classified as 'gold' coverage as starting point for upcoming cosmological applications. Distant cluster candidates were followed-up with moderately deep optical and near-infrared imaging in at least two bands to photometrically identify the cluster galaxy populations and obtain redshift estimates based on colors of simple stellar population models. We test and calibrate the most promising redshift estimation techniques based on the R−z and z−H colors for efficient distant cluster identifications and find a good redshift accuracy performance of the z−H color out to at least z∼1.5, while the redshift evolution of the R−z color leads to increasingly large uncertainties at z > ∼ 0.9. Photometrically identified high-z systems are spectroscopically confirmed with VLT/FORS 2 with a minimum of three concordant cluster member redshifts. We present first details of two newly identified clusters, ‡ Based on observations under program IDs 079.A-0634 and 085.A-0647 collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, and observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).§ Visiting astronomer at MPE.The X-ray luminous galaxy cluster population at 0.9 < z ≤ 1.6 as revealed by the XDCP 2 XDCP J0338.5+0029 at z=0.916 and XDCP J0027.2+1714 at z=0.959, and investigate the Xray properties of SpARCS J003550-431224 at z=1.335, which shows evidence for ongoing major merger activity along the line-of-sight. We provide X-ray properties and luminositybased total mass estimates for the full sample of 22 high-z clusters, of which 17 are at z ≥ 1.0 and 7 populate the highest redshift bin at z > 1.3. The median system mass of the sample is M 200 ≃ 2 × 10 14 M ⊙ , while the probed mass range for the distant clusters spans approximately (0.7-7)×10 14 M ⊙ . The majority (>70%) of the X-ray selected clusters show rather regular Xray morphologies, albeit in most cases with a discernible elongation along one axis. In contrast to local clusters, the z > 0.9 systems do mostly not harbor central dominant galaxies coincident with the X-ray centroid position, but rather exhibit significant BCG offsets from the X-ray center with a median value of about 50 kpc in projection and a smaller median luminosity gap to the second-ranked galaxy of ∆m 12 ≃ 0.3 mag. We estimate a fraction of cluster-associated NVSS 1.4 GHz radio sources of about 30%, preferentially located within 1 ′ from the X-ray center. This value sugge...