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 X-ray cluster,MS0451.6-0305, at z=0.5386. Spectral imaging data for the cluster areconsistent with an isothermal cluster of 10.0 - 10.6 +/-1.6 keV and an Feabundance of 0.32-0.40 +/-0.13 solar. The systematic uncertainties, arisingfrom calibration and model uncertainties, of the temperature determination arenearly the same size as the statistical uncertainties. We discuss the effectsof the ACIS absorption correction on the spectral fitting. The effects ofstatistics and fitting assumptions of 2-D models for the X-ray surfacebrightness are thoroughly explored. This cluster appears to be elongated and sowe quantify the effects of assuming an ellipsoidal gas distribution on the gasmass and the total gravitating mass estimates. These data are also jointly fitwith previous S-Z observations to obtain an estimate of the cluster's distanceassuming spherical symmetry. If we, instead, assume a Hubble constant, theX-ray and S-Z data are used together to test the consistency of an ellipsoidalgas distribution and to weakly constrain the intrinsic axis ratio. The massderived from the X-ray data is consistent with the weak lensing and opticalmasses. We confirm that this cluster is very hot and massive, furthersupporting the conclusion of previous analyses that the universe has a lowmatter density and that cluster properties, including iron abundances, have notevolved much since z~0.5. We discuss the possible detection of a faint, soft,extended component that may be the by-product of hierarchical structureformation