The Mass, Baryonic Fraction, and X-Ray Temperature of the Luminous, High-Redshift Cluster of Galaxies MS 0451.6–0305

We present new Chandra X-ray observations of the luminous and cosmologically significant X-ray cluster of galaxies, MS 0451.6-0305, at z = 0.5386. Spectral imaging data for the cluster are consistent with an isothermal cluster of (10.0-10.6) ± 1.6 keV, with an intracluster Fe abundance of (0.32-0.40) ± 0.13 solar. The systematic uncertainties, arising from calibration and model uncertainties, of the temperature determination are nearly the same size as the statistical uncertainties, since the time-dependent correction for absorption on the detector is uncertain for these data. We discuss the effects of this correction on the spectral fitting. The effects of statistics and fitting assumptions of two-dimensional models for the X-ray surface brightness are thoroughly explored. This cluster appears to be elongated, and so we quantify the effects of assuming an ellipsoidal gas distribution on the gas mass and the total gravitating mass estimates. These data are also jointly fitted with previous Sunyaev-Zeldovich observations to obtain an estimate of the cluster's distance (DA = 1219 ± 387 Mpc, statistical followed by systematic uncertainties) assuming spherical symmetry. If, instead, we assume a Hubble constant, the X-ray and Sunyaev-Zeldovich data are used together to test the consistency of an ellipsoidal gas distribution and to weakly constrain the intrinsic axis ratio. The mass derived from the X-ray data is consistent with the weak-lensing mass and is only marginally less than the mass determined from the optical velocities. We confirm that this cluster is very hot and massive, further supporting the conclusion of previous analyses that the universe has a low matter density and that cluster properties have not evolved much since z ~ 0.5. Furthermore, the presence of iron in this high-redshift cluster at an abundance that is the same as that of low-redshift clusters implies that there has been very little evolution of the cluster iron abundance since z ~ 0.5. We discuss the possible detection of a faint, soft, extended component that may be the by-product of hierarchical structure formation.