A Lensing Survey of Normal Clusters

We propose to finish our project to determine the amount and spatial distribution of dark matter in 10 X-ray selected ``normal'' clusters at z~0.2 using weak gravitational lensing. We will measure M/L vs radius, the radial mass density gradient, and the mass anisotropy of each cluster to a radius of 5 Mpc, which is large enough to probe non- virialized regions. Since these cluster properties depend upon cosmology, our measurements will be used to: (1) test cosmological models by comparing the program clusters with clusters found in numerical cosmological simulations, (2) determine the ratio of baryonic/dark matter in the clusters, which coupled with big bang nucleosynthesis results will yield an accurate estimate of Ω_m, and (3) compare our mass maps with other mass indicators such as X-ray luminosity to constrain the internal dynamics of the cluster. This program has already discovered that the cluster profiles are isothermal to r ~ 1 Mpc, further out than expected from most numerical simulations of these relatively low-mass systems. We have also discovered previously unknown large mass concentrations in regions without an obvious cluster.