We present a study of multiwavelength X-ray and weak lensing scaling relations for a sample of 50 clusters of galaxies. Our analysis combines Chandra and XMM-Newton data using an energy-dependent cross-calibration. After considering a number of scaling relations, we find that gas mass is the most robust estimator of weak lensing mass, yielding 15% ± 6% intrinsic scatter at r WL 500 (the pseudo-pressure Y X yields a consistent scatter of 22% ± 5%). The scatter does not change when measured within a fixed physical radius of 1 Mpc. Clusters with small brightest cluster galaxy (BCG) to X-ray peak offsets constitute a very regular population whose members have the same gas mass fractions and whose even smaller (<10%) deviations from regularity can be ascribed to line of sight geometrical effects alone. Cool-core clusters, while a somewhat different population, also show the same (<10%) scatter in the gas mass-lensing mass relation. There is a good correlation and a hint of bimodality in the plane defined by BCG offset and central entropy (or central cooling time). The pseudo-pressure Y X does not discriminate between the more relaxed and less relaxed populations, making it perhaps the more even-handed mass proxy for surveys. Overall, hydrostatic masses underestimate weak lensing masses by 10% on the average at r WL 500 ; but coolcore clusters are consistent with no bias, while non-cool-core clusters have a large and constant 15%-20% bias between r WL 2500 and r WL 500 , in agreement with N-body simulations incorporating unthermalized gas. For non-cool-core clusters, the bias correlates well with BCG ellipticity. We also examine centroid shift variance and power ratios to quantify substructure; these quantities do not correlate with residuals in the scaling relations. Individual clusters have for the most part forgotten the source of their departures from self-similarity.

We present measurements of surface brightness and colour profiles for the brightest cluster galaxies (BCGs) in a sample of 48 X-ray luminous galaxy clusters. These data were obtained as part of the Canadian Cluster Comparison Project (CCCP). The Kormendy relation of our BCGs is steeper than that of the local ellipticals, suggesting differences in the assembly history of these types of systems. We also find that while most BCGs show monotonic colour gradients consistent with a decrease in metallicity with radius, 25 per cent of the BCGs show colour profiles that turn bluer towards the centre (blue cores). We interpret this bluing trend as evidence for recent star formation. The excess blue light leads to a typical offset from the red sequence of 0.5 to 1.0 mag in (g − r ), thus affecting optical cluster studies that may reject the BCG based on colour. All of the blue-core BCGs are located within ∼10 kpc of the peak in the cluster X-ray emission. Furthermore, virtually all of the BCGs with recent star formation are in clusters that lie above the L x -T x relation. Based on photometry alone, these findings suggest that central star formation is a ubiquitous feature of BCGs in dynamically relaxed cool-core clusters. This implies that while active galactic nuclei (AGNs) and other heating mechanisms are effective at tempering cooling, they do not full compensate for the energy lost via radiation.

The Canadian Cluster Comparison Project is a comprehensive multi‐wavelength survey targeting 50 massive X‐ray selected clusters of galaxies to examine baryonic tracers of cluster mass and to probe the cluster‐to‐cluster variation in the thermal properties of the hot intra‐cluster medium. In this paper we present the weak lensing masses, based on the analysis of deep wide field imaging data obtained using the Canada–France–Hawaii Telescope. The final sample includes two additional clusters that were located in the field‐of‐view. We take these masses as our reference for the comparison of cluster properties at other wavelengths. In this paper we limit the comparison to published measurements of the Sunyaev–Zel'dovich effect. We find that this signal correlates well with the projected lensing mass, with an intrinsic scatter of 12 ± 5 per cent at ∼r2500, demonstrating it is an excellent proxy for cluster mass.

We use the suite of simulations presented by Poole et al. to examine global X‐ray and Sunyaev–Zel'dovich (SZ) observables for systems of merging relaxed X‐ray clusters. The time evolution of our merging systems' X‐ray luminosities, temperatures, total mass measures, SZ central Compton parameters and integrated SZ fluxes are presented and the resulting impact on their scaling relations examined. In all cases, and for all parameters, we observe a common time evolution: two rapid transient increases during first and second pericentric passage, with interceding values near or below their initial levels. This is in good qualitative agreement with previous idealized merger simulations, although we find several important differences related to the inclusion of radiative cooling in our simulations. These trends translate into a generic evolution in the scaling‐relation planes as well: a rapid transient roughly along the mass scaling relations, a subsequent slow drift across the scatter until virialization, followed by a slow evolution along and up the mass scaling relations as cooling recovers in the cluster cores. However, this drift is not sufficient to account for the observed scatter in the scaling relations. We also study the effects of mergers on several theoretical temperature measures of the intracluster medium: emission‐weighted measures (Tew), the spectroscopic‐like measure (Tsl) proposed by Mazzotta et al. and plasma model fits to the integrated spectrum of the system (Tspec). We find that Tsl tracks Tspec for the entire duration of our mergers, illustrating that it remains a good tool for observational comparison even for highly disturbed systems. Furthermore, the transient temperature increases produced during first and second pericentric passage are 15–40 per cent larger for Tew than for Tsl or Tspec. This suggests that the effects of transient temperature increases on σ8 and ΩM derived by Randall et al. are over estimated. Lastly, we examine the X‐ray SZ proxy proposed by Kravtsov, Vikhlinin & Nagai (2006) and find that the tight mass scaling relation they predict remains secure through the entire duration of a merger event, independent of projection effects.

We present a joint analysis of near‐ultraviolet (NUV) data from the GALEX (Galaxy Evolution Explorer) mission and (optical) colour profiles for a sample of seven brightest cluster galaxies (BCGs) in the Canadian Cluster Comparison Project. We find that every BCG, which has a blue rest‐frame UV colour, also shows a blue core in its optical colour profile. Conversely, BCGs that lack blue cores and show monotonic colour gradients typical of old elliptical galaxies are red in the UV. We interpret this as evidence that the NUV enhancement in the blue BCGs is driven by recent star formation and not from old evolved stellar populations such as horizontal branch stars. Furthermore, the UV enhancement cannot be from an active galactic nuclei (AGN) because the spatial extent of the blue cores is significantly larger than the possible contamination region due to a massive black hole. The recent star formation in the blue BCGs typically has an age less than 200 Myr and contributes mass fractions of less than a per cent. Although the sample studied here is small, we demonstrate, for the first time, a one‐to‐one correspondence between blue cores in elliptical galaxies (in particular BCGs) and a NUV enhancement observed using GALEX. The combination of this one‐to‐one correspondence and the consistently young age of recent star formation, coupled with additional correlations with the host cluster's X‐ray properties, strongly suggests that the star formation is fuelled by gas cooling out of the intracluster medium. In turn, this implies that any AGN heating of the intracluster medium in massive clusters only acts to reduce the magnitude of the cooling flow and once this flow starts, it is nearly always active. Collectively, these results suggest that AGN feedback in present‐day BCGs, while important, cannot be as efficient as suggested by the recent theoretical model by proposed by De Lucia et al.