ChandraandXMM-NewtonObservations of RDCS 1252.9-2927, A Massive Cluster atz=1.24

Abstract

We present deep Chandra and XMM-Newton observations of the galaxy cluster RDCS1252.9-2927, which was selected from the ROSAT Deep Cluster Survey (RDCS) and confirmed by extensive spectroscopy with the VLT at redshift z = 1.237. With the Chandra data, the X-ray emission from the intra-cluster medium is well resolved and traced out to 500 kpc, thus allowing a measurement of the physical properties of the gas with unprecedented accuracy at this redshift. We detect a clear 6.7 keV Iron K line in the Chandra spectrum providing a redshift within 1% of the spectroscopic one. By augmenting our spectroscopic analysis with the XMM-Newton data (MOS detectors only), we significantly narrow down the 1{sigma} error bar to 10% for the temperature and 30% for the metallicity, with best fit values kT = 6.0{sup +0.7}{sub -0.5} keV, Z = 0.36{sup +0.12}{sup -0.10}Z{sub {circle_dot}}. In the likely hypothesis of hydrostatic equilibrium, we measure a total mass of M{sub 500} = (1.9{+-}0.3)10{sup 14}h{sup -1}{sub 70} M{sub {circle_dot}} within R{sub {Delta}=500} {approx} 536 kpc. Overall, these observations imply that RDCS1252.9-2927 is the most X-ray luminous and likely the most massive bona-fide cluster discovered to date at z > 1. When combined with current samples of distantmore » clusters, these data lend further support to a mild evolution of the cluster scaling relations, as well the metallicity of the intra-cluster gas. Inspection of the cluster mass function in the current cosmological concordance model (h,{Omega}{sub m},{Omega}{sub {Lambda}}) = (0.7,0.3,0.7) and {sigma}{sub 8} = 0.7-0.8 shows that RDCS1252.9-2927 is an M* cluster at z = 1.24, in keeping with number density expectations in the RDCS survey volume.« less