Cosmological constraints from clusters rely on accurate gravitational mass estimates, which strongly depend on cluster gas temperature measurements. Therefore, systematic calibration differences may result in biased, instrument-dependent cosmological
constraints. This is of special interest in the light of the tension between the Planck results of the primary temperature anisotropies of the CMB and Sunyaev-Zeldovich plus X-ray cluster counts analyses. We quantify in detail the systematics and uncertainties of the cross-calibration of the effective area between five X-ray instruments, EPIC-MOS1/MOS2/PN onboard XMM-Newton and ACIS-I/S onboard Chandra, and the influence on temperature measurements. Furthermore, we assess the impact of the cross calibration uncertainties on cosmology. Using the HIFLUGCS sample, consisting of the 64 X-ray brightest galaxy clusters, we constrain the ICM temperatures through spectral fitting in the same, mostly isothermal, regions and compare them. Our work is an extension to a previous one using X-ray clusters by the IACHEC. Performing spectral fitting in the full energy band we find that best-fit temperatures determined with XMM-Newton/EPIC are significantly lower than Chandra/ACIS temperatures. We demonstrate that effects like multitemperature structure and different relative sensitivities of the instruments at certain energy bands cannot explain the observed differences. We conclude that using XMM-Newton/EPIC, instead of Chandra/ACIS to derive full energy band temperature profiles for cluster mass determination results in an 8% shift towards lower OmegaM values and <1% shift towards higher sigma8 values in a cosmological analysis of a complete sample of galaxy clusters. Such a shift is insufficient to significantly alleviate the tension between Planck CMB anisotropies and SZ plus XMM-Newton cosmological constraints.
Using Chandra data for a sample of 26 galaxy groups, we constrained the central cooling times (CCTs) of the ICM and classified the groups as strong cool-core (SCC), weak cool-core (WCC) and non-cool-core (NCC) based on their CCTs. The total radio lum
inosity of the brightest cluster galaxy (BCG) was obtained using radio catalog data and literature, which was compared to the CCT to understand the link between gas cooling and radio output. We determined K-band luminosities of the BCG with 2MASS data, and used it to constrain the masses of the SMBH, which were then compared to the radio output. We also tested for correlations between the BCG luminosity and the overall X-ray luminosity and mass of the group. The observed cool-core/non-cool-core fractions for groups are comparable to those of clusters. However, notable differences are seen. For clusters, all SCCs have a central temperature drop, but for groups, this is not the case as some SCCs have centrally rising temperature profiles. While for the cluster sample, all SCC clusters have a central radio source as opposed to only 45% of the NCCs, for the group sample, all NCC groups have a central radio source as opposed to 77% of the SCC groups. For clusters, there are indications of an anticorrelation trend between radio luminosity and CCT which is absent for the groups. Indications of a trend of radio luminosity with black hole mass observed in SCC clusters is absent for groups. The strong correlation observed between the BCG luminosity and the cluster X-ray luminosity/cluster mass weakens significantly for groups. We conclude that there are important differences between clusters and groups within the ICM cooling/AGN feedback paradigm.
