Temperature and Metallicity of a Massive X-Ray Cluster at Redshift 0.5

We present spectroscopic X-ray observations, obtained with the Advanced Satellite for Cosmology and Astrophysics (ASCA), of MS 0451. 6-0305, the most luminous cluster of galaxies and one of the most distant (z = 0. 54) in the Extended Medium-Sensitivity Survey (EMSS). We find that the hot gas in this cluster has a temperature of 10. 4 +/- 1. 2 keV, which is very hot but commensurate with its X-ray luminosity (2-10 keV rest frame) of 2. 2 x 10⁴5^ h₅0_^-2^ ergs s^-1^, if the relationship between Lₓ_ and Tₓ_ is the same at redshift 0. 5 as nearby. The iron abundance of this gas is 0. 15_-0. 12_^+0. 11^ solar, somewhat lower than, but consistent with, the iron abundance of hot gas in nearby clusters. The temperature of this gas, when combined with the image parameters of the ROSAT Position Sensitive Proportional Counter (PSPC) X-ray map and with the assumption that the gas is isothermal and in nearly hydrostatic equilibrium with the cluster gravitational potential, implies a hot gas mass of 4. 1 x 10¹3^ h₅0_^-5/2^ Hₛun_ and a total mass (including the dark matter) of 10¹5^ h₅0_^-1^ Hₛun) within a radius of 1 h₅0_^-1^ Mpc. The total mass is consistent with the mass estimated from gravitational lensing observations. The ratio of hot gas mass to the total mass is thus only ~4% (+/- 2%, conservatively), lower than the ratio of the gas to total mass in Coma or other clusters within the same physical scale. These observations are consistent with a picture of cluster evolution in which an early starburst phase provides most of the intracluster iron and intracluster gas, and a substantial fraction of the baryonic matter is initially associated with galaxies.