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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, C. J. Miller, R. C. Nichol, M. J. West, C. J. Conselice, H. Spinrad, D. Stern, K. Bundy

astro-pharXiv:astro-ph/0606075

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 6 galaxies within a 60 arcsec 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 Lx = 4.4 (+0.8,-0.6) x 1044 ergs/s over a 2 Mpc radial region. The measured Tx, which is the highest known for a 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.

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