DISCOVERY OF AN X-RAY-LUMINOUS GALAXY CLUSTER AT z = 1.4

摘要

We report the discovery of a massive, X-ray-luminous cluster of galaxies at z = 1.393, the most distant X-ray-selected cluster found to date. XMMU J2235.3 —2557 was serendipitously detected as an extended X-ray source in an archival XMM-Newton observation of NGC 7314. VLT FORS2 R- and z-band snapshot imaging reveals an overdensity of red galaxies in both angular and color spaces. The galaxy enhancement is coincident in the sky with the X-ray emission; the cluster red sequence at R—z approx= 2.1 identifies it as a high-redshift candidate. Subsequent FORS2 multiobject spectroscopy unambiguously confirms the presence of a massive cluster based on 12 concordant redshifts in the interval 1.38 < z < 1.40. The preliminary cluster velocity dispersion is 762 ± 265 km s~(-1). VLT ISAAC K_s- and J-band images underscore the rich distribution of red galaxies associated with the cluster. Based on a 45 ks XMM-Newton observation, we find that the cluster has an aperture-corrected unabsorbed X-ray flux of f_x = (3.6 ± 0.3) x 10~(-14) ergs cm~(-2) s~(-1), a rest-frame X-ray luminosity of L_x = (3.0 ± 0.2) x 10~(44) h_(70)~(-2) ergs s~(-1) (0.5-2.0 keV), and a temperature of kT = 6.0_(-1.8)~(+2.5) keV. Though XMMU J2235.3-2557 is likely the first confirmed z > 1 cluster found with XMM-Newton, the relative ease and efficiency of discovery demonstrates that it should be possible to build large samples of z > 1 clusters through the joint use of X-ray and large ground-based telescopes.