We have assembled a large sample of virialized systems, comprising 66 galaxy clusters, groups and elliptical galaxies with high‐quality X‐ray data. To each system we have fitted analytical profiles describing the gas density and temperature variation with radius, corrected for the effects of central gas cooling. We present an analysis of the scaling properties of these systems and focus in this paper on the gas distribution and M–TX relation. In addition to clusters and groups, our sample includes two early‐type galaxies, carefully selected to avoid contamination from group or cluster X‐ray emission. We compare the properties of these objects with those of more massive systems and find evidence for a systematic difference between galaxy‐sized haloes and groups of a similar temperature. We derive a mean logarithmic slope of the M–TX relation within R200 of 1.84 ± 0.06, although there is some evidence of a gradual steepening in the M–TX relation, with decreasing mass. We recover a similar slope using two additional methods of calculating the mean temperature. Repeating the analysis with the assumption of isothermality, we find the slope changes only slightly, to 1.89 ± 0.04, but the normalization is increased by 30 per cent. Correspondingly, the mean gas fraction within R200 changes from (0.13 ± 0.01) h  −3/2 70 to (0.11 ± 0.01) h  −3/2 70, for the isothermal case, with the smaller fractional change reflecting different behaviour between hot and cool systems. There is a strong correlation between the gas fraction within 0.3R200 and temperature. This reflects the strong (5.8σ) trend between the gas density slope parameter, β, and temperature, which has been found in previous work. These findings are interpreted as evidence for self‐similarity breaking from galaxy feedback processes, active galactic nuclei heating or possibly gas cooling. We discuss the implications of our results in the context of a hierarchical structure formation scenario.

Studies of the X-ray surface brightness profiles of clusters, coupled with theoretical considerations, suggest that the breaking of self-similarity in the hot gas results from an `entropy floor', established by some heating process, which affects the structure of the intracluster gas strongly in lower mass systems. Fitting analytical models for the radial variation in gas density and temperature to X-ray spectral images from the ROSAT PSPC and ASCA GIS, we derive gas entropy profiles for 20 galaxy clusters and groups. Scaling these profiles to coincide in the self-similar case, the lowest mass systems are found to have higher scaled entropy profiles than more massive systems. This appears to be due to a baseline entropy of 70-140 h50^-1/3 keV cm^2, depending on the extent to which shocks have been suppressed in low mass systems. The extra entropy may be present in all systems, but is detectable only in poor clusters, compared to the entropy generated by gravitational collapse. This excess entropy appears to be distributed uniformly with radius outside the central cooling regions. We determine the energy associated with this entropy floor, by studying the net reduction in binding energy of the gas in low mass systems, and find that it corresponds to a preheating temperature of ~0.3 keV. Since the relationship between entropy and energy injection depends upon gas density, we can combine the excesses of 70-140 keV cm^2 and 0.3 keV to derive the typical electron density of the gas into which the energy was injected. The resulting value of 1-3x10^-4 h50^1/2 cm-3, implies that the heating must have happened prior to cluster collapse but after a redshift z~7-10. The energy requirement is well matched to the energy from supernova explosions responsible for the metals which now pollute the intracluster gas.Comment: 15 pages, 10 figures, accepted for publication in MNRA

We use Chandra X-ray and Spitzer infrared (IR) observations to explore the active galactic nucleus (AGN) and starburst populations of XMMXCS J2215.9−1738 at z = 1.46, one of the most distant spectroscopically confirmed galaxy clusters known. The high-resolution X-ray imaging reveals that the cluster emission is contaminated by point sources that were not resolved in XMM-Newton observations of the system, and have the effect of hardening the spectrum, leading to the previously reported temperature for this system being overestimated. From a joint spectroscopic analysis of the Chandra and XMM-Newton data, the cluster is found to have temperature T = 4.1 +0.6 −0.9 keV and luminosity L X = (2.9244 erg s −1 , extrapolated to a radius of 2 Mpc. As a result of this revised analysis, the cluster is found to lie on the σ v -T relation, but the cluster remains less luminous than would be expected from self-similar evolution of the local L X -T relation. Two of the newly discovered X-ray AGNs are cluster members, while a third object, which is also a prominent 24 µm source, is found to have properties consistent with it being a high-redshift, highly obscured object in the background. We find a total of eight >5σ 24 µm sources associated with cluster members (four spectroscopically confirmed and four selected using photometric redshifts) and one additional 24 µm source with two possible optical/near-IR counterparts that may be associated with the cluster. Examining the Infrared Array Camera colors of these sources, we find that one object is likely to be an AGN. Assuming that the other 24 µm sources are powered by star formation, their IR luminosities imply star formation rates ∼100 M ⊙ yr −1 . We find that three of these sources are located at projected distances of <250 kpc from the cluster center, suggesting that a large amount of star formation may be taking place in the cluster core, in contrast to clusters at low redshift.

We present deep J and K s band photometry of 20 high redshift galaxy clusters between z = 0.8−1.5, 19 of which are observed with the MOIRCS instrument on the Subaru Telescope. By using nearinfrared light as a proxy for stellar mass we find the surprising result that the average stellar mass of Brightest Cluster Galaxies (BCGs) has remained constant at ∼ 9 × 10 11 M ⊙ since z ∼ 1.5. We investigate the effect on this result of differing star formation histories generated by three well known and independent stellar population codes and find it to be robust for reasonable, physically motivated choices of age and metallicity. By performing Monte Carlo simulations we find that the result is unaffected by any correlation between BCG mass and cluster mass in either the observed or model clusters. The large stellar masses imply that the assemblage of these galaxies took place at the same time as the initial burst of star formation. This result leads us to conclude that dry merging has had little effect on the average stellar mass of BCGs over the last 9 − 10 Gyr in stark contrast to the predictions of semi-analytic models, based on the hierarchical merging of dark matter haloes, which predict a more protracted mass build up over a Hubble time. We discuss however that there is potential for reconciliation between observation and theory if there is a significant growth of material in the intracluster light over the same period.