The Intracluster Medium in z > 1 Galaxy Clusters

The Chandra X-Ray Observatory was used to obtain a 190 ks image of three high-redshift galaxy clusters in one observation. The results of our analysis of these data are reported for the two z > 1 clusters in this Lynx field, which are the most distant known X-ray luminous clusters. Spatially extended X-ray emission was detected from both these clusters, indicating the presence of hot gas in their intracluster media. A fit to the X-ray spectrum of RX J0849+4452 at z = 1.26 yields a temperature of kT = 5.8 keV. Using this temperature and the assumption of an isothermal sphere, the total mass of RX J0849+4452 is found to be 4.0 × 10¹⁴ h M_☉ within r = 1 h Mpc. The T_X for RX J0849+4452 approximately agrees with the expectation based on its L_bol = 3.3 × 10⁴⁴ ergs s^-1 according to the low-redshift L_X-T_X relation. The very different distributions of X-ray-emitting gas and of the red member galaxies in the two z > 1 clusters, in contrast to the similarity of the optical/IR colors of those galaxies, suggests that the early-type galaxies mostly formed before their host clusters.