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

We construct a photometric catalogue of very faint galaxies (I < ∼ 25.5) using deep CCD images taken with the 4.2m William Herschel telescope taken of fields centred on two distant X-ray luminous clusters: 1455+22 (zcl = 0.26) and 0016+16 (zcl = 0.55). Using a non-parametric procedure developed by Kaiser & Squires (1993), we analyse the statistical image distortions in our samples 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 Ho=50 kms sec Mpc, qo = 0.5) with a mean signal to noise per resolution element of 17 and 14. Although the absolute normalisation of these mass maps depends on the assumed redshift distribution of the I < ∼ 25.5 field galaxies used as probes, the maps should be reliable on a relative scale and will trace the cluster mass regardless of whether it is baryonic or non-baryonic. We compare our 2-D mass distributions on scales up to ∼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.