Preprint typeset using L ATEX style emulateapj v. 08/13/06 THE XMM CLUSTER SURVEY: THE DYNAMICAL STATE OF XMMXCS J2215.9 − 1738 AT z = 1.457

We present new spectroscopic observations of the most distant X-ray selected galaxy cluster currently known, XMMXCS J2215.9−1738 at z = 1.457, obtained with the DEIMOS instrument at the W. M. Keck Observatory, and the FORS2 instrument on the ESO Very Large Telescope. Within the cluster virial radius, as estimated from the cluster X-ray properties, we increase the number of known spectroscopic cluster members to 17 objects, and calculate the line of sight velocity dispersion of the cluster to be 580± 140 km s. We find mild evidence that the velocity distribution of galaxies within the virial radius deviates from a single Gaussian. We show that the properties of J2215.9−1738 are inconsistent with self-similar evolution of local X-ray scaling relations, finding that the cluster is underluminous given its X-ray temperature, and that the intracluster medium contains ∼ 2− 3 times the kinetic energy per unit mass of the cluster galaxies. These results can perhaps be explained if the cluster is observed in the aftermath of an off-axis merger. Alternatively, heating of the intracluster medium through supernovae and/or Active Galactic Nuclei activity, as is required to explain the observed slope of the local X-ray luminosity–temperature relation, may be responsible. Subject headings: X-rays: galaxies: clusters — galaxies: clusters: individual (XMMXCS J2215.9−1738)