Gravitational lensing of distant field galaxies by rich clusters - II. Cluster mass distributions

Using a non-parametric procedure developed by Kaiser \& Squires (1993), weanalyse 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 theclusters. The mass maps of 1455+22 and 0016+16 are presented at effectiveresolutions 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 17and 14. We compare our 2-D mass distributions on scales up to $\sim$1 Mpc withthose defined by the spatial distribution of colour-selected cluster membersand from deep high resolution X-ray images of the hot intracluster gas. Despitethe different cluster morphologies, one being cD-dominated and the other not,in both cases the form of the mass distribution derived from the lensing signalis strikingly similar to that traced by both the cluster galaxies and the hotX-ray gas. We find some evidence for a greater central concentration of darkmatter with respect to the galaxies. The overall similarity between thedistribution of total mass and that defined by the baryonic components presentsa significant new observational constraint on the nature of dark matter and theevolutionary history of rich clusters.Comment: 13 pages (no figures), LaTex (MN style), postscript figures available via anonymous ftp in users/irs/figs/paper2.tar.gz on astro.caltech.edu, PAL-IRS-