Weak gravitational lensing by cluster of galaxies

I present a set of weak lensing measurements of a set of ∼40 highly X-ray luminous clusters of galaxies. The clusters were observed with either 2k monolithic CCDs or with the UH8k mosaic CCD camera, or both. The weak shear due to gravitational lensing was estimated using recently developed techniques to correct for the effects of realistic point spread functions and to optimally weigh the contribution of each galaxy to the final shear estimate.; The weak lensing results are presented in the form of maps of the reconstructed dimensionless surface density kappa and plots showing the radial cluster mass profiles. Two-color, V- and I-band galaxy photometry is used to isolate early-type galaxies and make predictions for the surface density distribution in the observed fields. The predicted and observed maps of kappa are correlated in various ways to derive values for the mass to (early type galaxy) light ratios in each cluster field. The relative amount and distribution of light and mass show significant differences from cluster to cluster and is probably related to the dynamical state of a cluster. The average mass-to-light ratio of the clusters indicates a low-density Universe with O0 ≃ 0.25. The mass measurements are also used to construct the first cluster mass function based on weak gravitational lensing data.; A Hubble Space Telescope mosaic covering the central ∼1h --1 Mpc of the rich cluster Abell 1689 is analyzed in a similar way as for the ground-based data. A highly significant mass peak, strongly correlated with the galaxy light distribution, is recovered, and the HST cluster mass estimate is shown to be consistent with estimates from ground-based imaging.; It is demonstrated that weak lensing measurements, preferably in combination with color. information from multi-band galaxy photometry, can be used to identify new cluster candidates at high redshifts.; A measurement of the net shear in ∼20' UH8k fields is used to estimate the shear variance due to weak lensing by large-scale structures along the line of sight.