A Deep Look at the Most Distant X-Ray Clusters

We present highlights from a study of galaxy populations and the intracluster medium (ICM) in three galaxy clusters at z > 1.2, the most distant X-ray luminous clusters currently known. Clusters are homogeneously selected from the ROSAT Deep Cluster Surveys (RDCS) which contains more than 100 spectroscopically confirmed clusters out to z ∼eq 1.3. Deep Chandra observations of two clusters at z ∼eq 1.26 have allowed for the first time physical parameters of the ICM to be measured at z > 1 and the morphology of the X-ray gas to be compared with the spatial distribution of the red member galaxies. The homogeneity of the spectrophotometric properties of early type galaxies in different clusters at z > 1.2 fits naturally into a scenario where their stellar populations formed at z ≳ 3, most likely before their host clusters.