We present deep Chandra and XMM-Newton observations of the galaxy cluster RDCS 1252.9-2927, which was selected from the ROSAT Deep Cluster Survey (RDCS) and confirmed by extensive spectroscopy with the Very Large Telescope at redshift z=1.237. With the Chandra data, the X-ray emission from the intracluster 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 σ error bar to 10% for the temperature and 30% for the metallicity, with best-fit values kT=6.0+0.7-0.5 keV, Z=0.36+0.12-0.10Zsolar. On the likely hypothesis of hydrostatic equilibrium, we measure a total mass of M500=(1.9+/-0.3)×1014h-170Msolar within R∆=500~=536 kpc. Overall, these observations imply that RDCS 1252.9-2927 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 distant clusters, these data lend further support to a mild evolution of the cluster scaling relations, as well the metallicity of the intracluster gas. Inspection of the cluster mass function in the current cosmological concordance model (h,Ωm,ΩΛ)=(0.7,0.3,0.7) and σ8=0.7-0.8 shows that RDCS 1252.9-2927 is an M* cluster at z=1.24, in keeping with number density expectations in the RDCS survey volume.Based in part on observations obtained at the European Southern Observatory using the ESO Very Large Telescope on Cerro Paranal (ESO program 166.A-0701).
The Astronomical Journal
- Pub Date:
- January 2004
- Cosmology: Observations;
- Galaxies: Clusters: General;
- galaxies: clusters: individual (RDCS 1252.9-2927);
- 9 pages, 1 color figure (fig6.jpg). The Astronomical Journal in press (Jan 2004). Full resolution preprint available at http://www.eso.org/~prosati/RDCS1252/