Serendipitous XMM-Newton discovery of a cluster of galaxies at z=0.28

Abstract

We report the discovery of a galaxy cluster serendipitously detected as an extended X-ray source in an offset observation of the group NGC 5044. The cluster redshift, z=0.281, determined from the optical spectrum of the brightest cluster galaxy, agrees with that inferred from the X-ray spectrum using the Fe K alpha complex of the hot ICM (z=0.27 +/- 0.01). Based on the 50 ks XMM observation, we find that within a radius of 383 kpc the cluster has an unabsorbed X-ray flux, f_X (0.5-2 keV) = 3.34 (+0.08, -0.13) x 10^{-13} erg/cm^2/s, a bolometric X-ray luminosity, L_X = 2.21 (+0.34, -0.19) x 10^{44} erg/s, kT = 3.57 +/- 0.12 keV, and metallicity, 0.60 +/- 0.09 solar. The cluster obeys the scaling relations for L_X and T observed at intermediate redshift. The mass derived from an isothermal NFW model fit is, M_vir = 3.89 +/- 0.35 x 10^{14} solar masses, with a concentration parameter, c = 6.7 +/- 0.4, consistent with the range of values expected in the concordance cosmological model for relaxed clusters. The optical properties suggest this could be a ``fossil cluster''.

arXiv comment5 pages, 4 colour figures, accepted for publication in ApJ

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• The XMM Cluster Survey: X-ray analysis methodology
• The Galaxy Cluster Concentration-Mass Scaling Relation
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• Internal dynamics of Abell 2254: a merging galaxy cluster with a clumpy, diffuse radio emission
• Estimate of the total mechanical feedback energy from galaxy cluster-centered black holes: implications for black hole evolution, cluster gas fraction and entropy
• Constraints on the winds of hot subdwarf stars from X-ray observations of two sdB binaries with compact companions: CD -30 11223 and PG 1232-136
• XMM-Newton observation of the cluster ZW 1305.4+2941 in the field SA 57
• Evolutionary properties of the low-luminosity galaxy population in the NGC5044 Group