The Second Most Distant Cluster of Galaxies in the Extended Medium Sensitivity Survey
Abstract
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+/-0.20.3×1013 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+/-1.50.8×1014 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<z<0.9 and compare it with temperature functions at lower redshifts, showing that the evolution of the temperature function is relatively modest. Supplementing our high-redshift sample with other data from the literature, we demonstrate that neither the cluster luminosity-temperature relation, nor cluster metallicities, nor the cluster gas fraction has detectably evolved with redshift. The very modest degree of evolution in the luminosity-temperature relation inferred from these data is inconsistent with the absence of evolution in the X-ray luminosity functions derived from ROSAT cluster surveys if a critical density structure formation model is assumed.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 1999
- DOI:
- 10.1086/308101
- Bibcode:
- 1999ApJ...527..525D
- Keywords:
-
- COSMOLOGY: OBSERVATIONS;
- COSMOLOGY: DARK MATTER;
- GALAXIES: CLUSTERS: INDIVIDUAL (MS 1137.5+6625);
- GALAXIES: INTERGALACTIC MEDIUM;
- X-RAYS: GALAXIES;
- Cosmology: Observations;
- Cosmology: Dark Matter;
- galaxies: clusters: individual (MS 1137.5+6625);
- Galaxies: Intergalactic Medium;
- X-Rays: Galaxies