The XMM Cluster Survey: A Massive Galaxy Cluster at z = 1.45

S. A. Stanford, A. K. Romer, K. Sabirli, M. Davidson, M. Hilton, P. T. P. Viana, C. A. Collins, S. T. Kay, A. R. Liddle, R. G. Mann, R. H. Miller, R. C. Nichol, M. West, C. J. Conselice, H. Spinrad, D. Stern, K. Bundy

Abstract
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^+2.7_-1.8 keV (90% confidence); if there is an undetected central X-ray point source, then kT=6.5^+2.6_-1.8 keV. The bolometric X-ray luminosity is L_X=4.4^+0.8_-0.6×10⁴⁴ 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.

The Astrophysical Journal Letters
Volume 646, Page L13
July 2006

DOI: 10.1086/506449