The XMM cluster survey: A massive galaxy cluster at z = 1.45

We report the discovery of XMMXCS J2215.9-1738, a massive galaxy cluster at z = 1.45, which was found in the XMM Cluster Survey. The cluster candidate was initially identified as an extended X-ray source in archival XMM data. Optical spectroscopy shows that six galaxies within a ∼60″ diameter region lie at z = 1.45 ± 0.01. Model fits to the X-ray spectra of the extended emission yield kT = 7.4-1.8+2.7 keV (90% confidence); if there is an undetected central X-ray point source, then kT = 6.5 -1.8+2.6 keV. The bolometric X-ray luminosity is L x = 4.4-0.6+0.8 × 1044 ergs s-1 over a 2 Mpc radial region. The measured Tx, which is the highest for any known cluster at z > 1, suggests that this cluster is relatively massive for such a high redshift. The redshift of XMMXCS J2215.9-1738 is the highest currently known for a spectroscopically confirmed cluster of galaxies. © 2006. The American Astronomical Society. All rights reserved.