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, which was found z = 1.45 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 similar to 60 '' diameter region lie at. z p 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). The bolometric X-ray luminosity is L-x-0.6(+0.8) x 10(44) ergs s(-1) over a 2 Mpc radial region. The measured T-x, 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 of J2215.9-1738 is the highest currently known for a spectroscopically confirmed cluster of galaxies.