The Second Most Distant Cluster of Galaxies in the Extended Medium Sensitivity Survey

Astronomy and Astrophysics – Astronomy

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Cosmology: Observations, Cosmology: Dark Matter, Galaxies: Clusters: Individual (Ms 1137.5+6625), Galaxies: Intergalactic Medium, X-Rays: Galaxies

Scientific paper

We report on our ASCA, Keck, and ROSAT observations of MS 1137.5+6625, the second most distant cluster of galaxies in the Einstein Extended Medium Sensitivity Survey (EMSS), at redshift 0.78. We now have a full set of X-ray temperatures, optical velocity dispersions, and X-ray images for a complete, high-redshift sample of clusters of galaxies drawn from the EMSS. Our ASCA observations of MS 1137.5+6625 yield a temperature of 5.7+2.1-1.1 keV and a metallicity of 0.43+0.40-0.37 solar, with 90% confidence limits. Keck II spectroscopy of 22 cluster members reveals a velocity dispersion of 884+185-124 km s-1. This cluster is the most distant in the sample with a detected iron line. We also derive a mean abundance at z=0.8 by simultaneously fitting X-ray data for the two z=0.8 clusters, and obtain an abundance of ZFe=0.33+/-0.260.23. Our ROSAT observations show that MS 1137.5+6625 is regular and highly centrally concentrated. Fitting of a β model to the X-ray surface brightness yields a core radius of only 71 h-1 kpc (q0=0.1) with β=0.70+/-0.450.15. The gas mass interior to 0.5 h-1 Mpc is thus 1.2+/-0.20.3x1013 h-5/2 Msolar (q0=0.1). If the cluster's gas is nearly isothermal and in hydrostatic equilibrium with the cluster potential, the total mass of the cluster within this same region is 2.1+/-1.50.8x1014 h-1 Msolar, giving a gas fraction of 0.06+/-0.04 h-3/2. This cluster is the highest redshift EMSS cluster showing evidence for a possible cooling flow (~20-400 Msolar yr-1). The velocity dispersion, temperature, gas fraction, and iron abundance of MS 1137.5+6625 are all statistically the same as those properties in lower redshift clusters of similar luminosity. With this cluster's temperature now in hand, we derive a high-redshift temperature function for EMSS clusters at 0.5

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