Discovery of an X-Ray-luminous Galaxy Cluster at <i>z</i> = 1.4

Abstract

We report the discovery of a massive, X-ray-luminous cluster of galaxies at\nz=1.393, the most distant X-ray-selected cluster found to date. XMMU\nJ2235.3-2557 was serendipitously detected as an extended X-ray source in an\narchival XMM-Newton observation of NGC 7314. VLT-FORS2 R and z band snapshot\nimaging reveals an over-density of red galaxies in both angular and color\nspaces. The galaxy enhancement is coincident in the sky with the X-ray\nemission; the cluster red sequence at R-z ~ 2.1 identifies it as a\nhigh-redshift candidate. Subsequent VLT-FORS2 multi-object spectroscopy\nunambiguously confirms the presence of a massive cluster based on 12 concordant\nredshifts in the interval 1.38&lt;z&lt;1.40. The preliminary cluster velocity\ndispersion is 762+/-265 km/s. VLT-ISAAC Ks and J band images underscore the\nrich distribution of red galaxies associated with the cluster. Based on a 45 ks\nXMM-Newton observation, we find the cluster has an aperture-corrected,\nunabsorbed X-ray flux of f_X = (3.6 +/- 0.3) x 10^{-14} erg/cm^2/s, a\nrest-frame X-ray luminosity of L_X = (3.0 +/- 0.2) x 10^{44} h_70^{-2} erg/s\n(0.5--2.0 keV), and a temperature of kT=6.0 (+2.5, -1.8) keV. Though XMMU\nJ2235.3-2557 is likely the first confirmed z&gt;1 cluster found with XMM-Newton,\nthe relative ease and efficiency of discovery demonstrates that it should be\npossible to build large samples of z&gt;1 clusters through the joint use of X-ray\nand large, ground-based telescopes.\n