| Gravitational lensing can be used to directly probe the quantity and distribution of dark matter, thus making it a powerful tool in astrophysics. In this thesis, I introduce the basics of gravitational lensing, and in particular weak gravitational lensing. Weak lensing is a statistical tool which allows the study of ensemble-averaged properties for a population of objects. I discuss two observational projects that use weak lensing to map dark matter distributions on different scales. The first project is a study of the mass distribution and mass-to-light ratios of galaxy groups. The second is a galaxy-galaxy lensing study of galaxy-sized dark matter halos.;I find that the mass-to-light ratio for a sample of galaxy groups is independent of radius, but is a function of the halo mass. This may indicate that groups of mass ∼1013 M⊙ mark the divide between the actively star forming field environment, and the passively evolving cluster regime. Our study of galaxy halos using early data from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) allows us to estimate the characteristic velocity dispersion for galaxy halos at a redshift of z ∼0.3. We also present evidence that galaxy dark matter halos may be elliptical rather than spherical. Future galaxy lensing results from the final CFHTLS data should allow us to determine accurately the dark matter mass profile and halo shape, thus providing important constraints on dark matter properties. |
