The environmental dependence of the stellar-mass-size relation in STAGES galaxies

We present the stellar-mass-size relations for elliptical, lenticular and spiral galaxies in the field and cluster environments using Hubble Space Telescope/Advanced Camera for Surveys imaging and data from the Space Telescope A901/2 Galaxy Evolution Survey. We use a large sample of similar to 1200 field and cluster galaxies and a sub-sample of cluster core galaxies, and quantify the significance of any putative environmental dependence on the stellar-mass-size relation. For elliptical, lenticular and high-mass (logM*/M(circle dot) > 10) spiral galaxies we find no evidence to suggest any such environmental dependence, implying that internal drivers are governing their size evolution. For intermediate-/low-mass spirals (logM(*)/M(circle dot) < 10) we find evidence, significant at the 2 sigma level, for a possible environmental dependence on galaxy sizes: the mean effective radius <(a)over bar>(e) for lower mass spirals is similar to 15-20 per cent larger in the field than in the cluster. This is due to a population of low-mass large-a(e) field spirals that are largely absent from the cluster environments. These large-a(e) field spirals contain extended stellar discs not present in their cluster counterparts. This suggests that the fragile extended stellar discs of these spiral galaxies may not survive the environmental conditions in the cluster. Our results suggest that internal physical processes are the main drivers governing the size evolution of galaxies, with the environment possibly playing a role affecting only the discs of intermediate-/low-mass spirals.