The X‐ray properties of a sample of 11 high‐redshift (0.6 < z < 1.0) clusters observed with Chandra and/or XMM–Newton are used to investigate the evolution of the cluster scaling relations. The observed evolution in the normalization of the L–T, M–T, Mg–T and M–L relations is consistent with simple self‐similar predictions, in which the properties of clusters reflect the properties of the Universe at their redshift of observation. Under the assumption that the model of self‐similar evolution is correct and that the local systems formed via a single spherical collapse, the high‐redshift L–T relation is consistent with the high‐z clusters having virialized at a significantly higher redshift than the local systems. The data are also consistent with the more realistic scenario of clusters forming via the continuous accretion of material. The slope of the L–T relation at high redshift (B= 3.32 ± 0.37) is consistent with the local relation, and significantly steeper than the self‐similar prediction of B= 2. This suggests that the same non‐gravitational processes are responsible for steepening the local and high‐z relations, possibly occurring universally at z≳ 1 or in the early stages of the cluster formation, prior to their observation. The properties of the intracluster medium at high redshift are found to be similar to those in the local Universe. The mean surface‐brightness profile slope for the sample is β= 0.66 ± 0.05, the mean gas mass fractions within R2500(z) and R200(z) are 0.069 ± 0.012 and 0.11 ± 0.02, respectively, and the mean metallicity of the sample is 0.28 ± 0.11 Z⊙.

We present an analysis of Chandra observations of two high-redshift clusters of galaxies, Cl J1113.1À2615 at z ¼ 0:725 and Cl J0152.7À1357 at z ¼ 0:833. We find Cl J1113.1À2615 to be morphologically relaxed with a temperature of kT ¼ 4:3 þ0:5 À0:4 keV and a mass (within the virial radius) of 4:3 þ0:8 À0:7 Â 10 14 M . Cl J0152.7À1357, by contrast, is resolved into a northern and southern subcluster, each massive and X-rayluminous, in the process of merging. The temperatures of the subclusters are found to be 5:5 þ0:9 À0:8 and 5:2 þ1:1 À0:9keV, respectively, and we estimate their respective masses to be 6:1 þ1:7 À1:5 Â 10 14 and 5:2 þ1:8 À1:4 Â 10 14 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 ¼ 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.

Deep XMM-Newton and Chandra observations of Cl J1226.9+3332 at z ¼ 0:89 have enabled the most detailed X-ray mass analysis of any such high-redshift galaxy cluster. The XMM-Newton temperature profile of the system shows no sign of central cooling, with a hot core and a radially declining profile. A temperature map shows asymmetry with a hot region that appears to be associated with a subclump of galaxies at the cluster redshift but is not visible in the X-ray surface brightness. This is likely to be the result of a merger event in the cluster but does not appear to significantly affect the overall temperature profile. The XMM-Newton temperature profile and combined Chandra and XMM-Newton emissivity profile allowed precise measurements of the global properties of Cl J1226.9+3332. Within an overdensity radius of 500 times the critical density at z ¼ 0:89 (R 500 ), we find kT ¼ 10:4 AE 0:6 keV, Z ¼ 0:16 AE 0:05 Z , and M ¼ 5:2 þ1:0 À0:8 ; 10 14 M . We obtain profiles of the metallicity, entropy, cooling time, and gas fraction and find a high concentration parameter for the total density profile of the system. The global properties are compared with the local L-T and M-T relations, and we are able to make the first observational test of the predicted evolution of the Y X -M 500 relation. We find that departures from these scaling relations are most likely caused by an underestimate of the total mass by $30% in the X-ray hydrostatic mass analysis due to the apparent recent or ongoing merger activity.

The WARPS (Wide Angle ROSAT Pointed Survey) team reviews the properties and history of discovery of ClJ0152.7-1357, an X-ray luminous, rich cluster of galaxies at a redshift of z = 0.833. At L X = 8 × 10 44 h −2 50 erg s −1 (0.5 − 2.0 keV) ClJ0152.7-1357 is the most X-ray luminous cluster known at redshifts z > 0.55. The high X-ray luminosity of the system suggests that massive clusters may begin to form at redshifts considerably greater than unity. This scenario is supported by the high degree of optical and X-ray substructure in ClJ0152.7-1357, which is similarly complex as that of other X-ray selected clusters at comparable redshift and consistent with the hypothesized picture of cluster formation by mass infall along large-scale filaments.X-ray emission from ClJ0152.7-1357 was detected already in 1980 with the EINSTEIN IPC. However, because the complex morphology of the emission caused its significance to be underestimated, the corresponding source was not included in the cluster sample of the EINSTEIN Extended Medium Sensitivity Survey (EMSS) and hence not previously identified. Simulations of the EMSS source detection and selection procedure performed by us suggest a general, mild bias of the EMSS cluster sample against X-ray luminous clusters with pronounced substructure.If highly unrelaxed, merging clusters are common at intermediate to high redshift (as is suggested by the current data) they could create a bias in some samples as the morphological complexity of mergers may cause them to fall below the flux limit of surveys that make the implicit or explicit assumption of a unimodal spatial source geometry. Conversely, the enhanced X-ray luminosity of mergers might cause them to, temporarily, rise above the flux limit. Either effect could lead to erroneous conclusions about the evolution of the comoving cluster space density. A high fraction of morphologically complex clusters at high redshift would also call into question the validity of evolutionary studies (and, specifically, cosmological conclusions) which implicitly or explicitly assume that the systems under investigation are virialized.

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 × 1015 M⊙ is derived, with a gas mass fraction of 12 ± 5 per cent (for a Λ cold dark matter cosmology and H0= 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× 1045 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 × 10−5 for ΩM= 1 and 0.64 for ΩM= 0.3, making ΩM= 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.