Deep XMM-Newton and Chandra Observations of Cl J1226.9+3332: A Detailed X-Ray Mass Analysis of a z = 0.89 Galaxy Cluster

摘要

Deep XMM-Newton and Chandra observations of Cl J1226.9+3332 at z = 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 = 0.89 (R500), we find kT = 10.4 ± 0.6 keV, Z = 0.16 ± 0.05 Z☉, and M = 5.2 × 1014 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 YX-M500 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.