X-ray Mass Estimates at $z\sim0.3$ for the CNOC Cluster Sample

Abstract

Results are presented from the analysis of ROSAT HRI and PSPC observations of the CNOC subsample of the EMSS high redshift galaxy clusters. X-ray surface brightness profiles of 14 clusters with $0.17 < z < 0.55$ are constructed and fit to isothermal $\beta$ models. Where possible, we use both the HRI and PSPC data to constrain the fit. Under the assumptions of isothermality, hydrostatic equilibrium, and spherical symmetry, we derive total X-ray masses within a range of radii from 141 to $526 h^{-1}_{100}$ kpc. These masses are compared with both the dynamical masses obtained from galaxy velocities and the projected masses from published gravitational lensing studies. We find no systematic bias between X-ray and dynamical methods across the sample, with an average $M_{Dyn}/M_X=1.04\pm0.07$, although individual clusters exhibit mass discrepancies up to a factor of 2. We estimate that the systematic effects due to cooling flows, non-equilibrium systems and temperature gradients affect the average mass ratio by no more than $15-20%$. Weak gravitational lensing masses appear to be systematically higher than X-ray results by factors of $\sim50%$, while strong lensing estimates show larger discrepancies (factors of $\sim2.5$). However, these comparisons are complicated by the need to extrapolate the X-ray data to larger or smaller radii. X-ray derived cluster gas masses are calculated, from which we obtain a cluster baryon fraction of $\sim5%h^{-3/2}_{100}$, yielding $\Omega_0 \sim0.3h^{-1/2}_{100}$.