Linking galaxies with their dark matter halos

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We know that galaxies live in extended dark matter halos, but the size and shape of these halos are poorly constrained. Dark matter does not emit light which makes studying its properties particularly difficult. However, the amount and distribution of dark matter can be inferred by its gravitational influence using gravitational lensing. Linking observed galaxies to the halos in which they live can help us to constrain different aspects of galaxy formation, for example the efficiency of star formation.This proposal focusses on measuring the gravitational lensing, hence dark matter properties, at two different mass scales. The first study concerns determining the dark matter properties of galaxy-sized objects, and correlating the dark matter properties with the observed, luminous properties of the galaxies. The second study is related to galaxy groups. Galaxy groups are small collections of galaxies which are gravitationally bound. Most galaxies in the local universe live in galaxy groups, but their properties are relatively poorly understood compared to galaxy clusters and individual galaxies, because they are difficult to identify on the sky. I propose to study these systems using ground- and space-based optical imaging, combined with complementary data at different wavelengths in order to better understand the relationship between the dark and luminous components of galaxies and galaxy groups.