Gravitational Lensing of Distant Field Galaxies by Rich Clusters: II. -- Cluster Mass Distributions

Using a non-parametric procedure developed by Kaiser \& Squires (1993), we analyse the statistical image distortions of faint field galaxies to $I\ls25.5$ in two distant X-ray luminous clusters 1455+22 ($z_{cl}=0.26$) and 0016+16 ($z_{cl}=0.55$) to derive two dimensional projected mass distributions for the clusters. The mass maps of 1455+22 and 0016+16 are presented at effective resolutions of 135 kpc and 200 kpc respectively (for $H_o$=50 kms sec$^{-1}$ Mpc$^{-1}$, $q_o=0.5$) with a mean signal to noise per resolution element of 17 and 14. We compare our 2-D mass distributions on scales up to $\sim$1 Mpc with those defined by the spatial distribution of colour-selected cluster members and from deep high resolution X-ray images of the hot intracluster gas. Despite the different cluster morphologies, one being cD-dominated and the other not, in both cases the form of the mass distribution derived from the lensing signal is strikingly similar to that traced by both the cluster galaxies and the hot X-ray gas. We find some evidence for a greater central concentration of dark matter with respect to the galaxies. The overall similarity between the distribution of total mass and that defined by the baryonic components presents a significant new observational constraint on the nature of dark matter and the evolutionary history of rich clusters.