The second most distant cluster of galaxies in the extended medium sensitivity survey

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 Sen sitivity Survey (EMSS), at redshift 0.78. We now have a full set of X-ray t emperatures, 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(-1.1)(+2.1) ke V and a metallicity of 0.43(-0.37)(+0.40) solar, with 90% confidence limits . Keck II spectroscopy of 22 cluster members reveals a velocity dispersion of 884(-124)(+185) 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 s imultaneously fitting X-ray data for the two z = 0.8 clusters, and obtain a n abundance of Z(Fe) = 0.33 +/- (0.26)(0.23). Our ROSAT observations show t hat MS 1137.5 + 6625 is regular and highly centrally concentrated. Fitting of a beta model to the X-ray surface brightness yields a core radius of onl y 71 h(-1) kpc (q(0) = 0.1) with beta = 0.70 +/- (0.45)(0.15). The gas mass interior to 0.5 h(-1) Mpc is thus 1.2 +/- (0.2)(0.3) x 10(13) h(-5/2) M. ( q(0) = 0.1). If the cluster's gas is nearly isothermal and in hydrostatic e quilibrium with the cluster potential, the total mass of the cluster within this same region is 2.1 +/- (1.5)(0.8) x 10(14) h(-1) M., giving a gas fra ction of 0.06 +/- 0.04 h(-3/2). This cluster is the highest redshift EMSS c luster showing evidence for a possible cooling flow (similar to 20-400 M. y r(-1)). The velocity dispersion, temperature, gas fraction, and iron abunda nce of MS 1137.5 + 6625 are all statistically the same as those properties in lower redshift dusters of similar luminosity. With this cluster's temper ature now in hand, we derive a high-redshift temperature function for EMSS dusters at 0.5 < z < 0.9 and compare it with temperature functions at lower redshifts, showing that the evolution of the temperature function is relat ively modest. Supplementing our high-redshift sample with other data from t he literature, we demonstrate that neither the cluster luminosity-temperatu re relation, nor cluster metallicities, nor the cluster gas fraction has de tectably evolved with redshift. The very modest degree of evolution in the luminosity-temperature relation inferred from these data is inconsistent wi th the absence of evolution in the X-ray luminosity functions derived from ROSAT cluster surveys if a critical density structure formation model is as sumed.