Program: GN-2016A-FT-18

We have recently discovered a population of large, low surface brightness galaxies in the Coma cluster. These "ultra diffuse galaxies" (UDGs) have the sizes of L* galaxies but the stellar masses of dwarf galaxies. Using 20 hr integrations with Keck+DEIMOS, we have recently succeeded in measuring the kinematics of three of these UDGs. Surprisingly they span a very large range, from 20 km/s to 80 km/s (!). The interpretation is limited by the depth of the available imaging: the galaxies are clearly detected in 5 min integrations on the Canada France Hawaii Telescope, but it is difficult to measure their properties. Here we propose deep imaging with GMOS-N to remedy this situation, and to augment the deep spectra that we already have. The goals are to: 1) measure accurate effective radii, 2) measure stellar surface density profiles and total stellar masses, and 3) assess whether the galaxies show distortions due to tidal effects. We will publish these data immediately after they are taken, in combination with the Keck spectra.