Linking the Structural Properties of Galaxies and their Star Formation
  Histories with STAGES
  We study the links between star formation history and structure for a large
mass-selected galaxy sample at 0.05 < z_phot < 0.30. The galaxies inhabit a
very broad range of environments, from cluster cores to the field. Using HST
images, we quantify their structure following Hoyos et al. (2012), and divide
them into disturbed and undisturbed. We also visually identify mergers.
Additionally, we provide a quantitative measure of the degree of disturbance
for each galaxy ("roughness"). The majority of elliptical and lenticular
galaxies have relaxed structure, showing no signs of ongoing star formation.
Structurally-disturbed galaxies, which tend to avoid the lowest-density
regions, have higher star-formation activity and younger stellar populations
than undisturbed systems. Cluster spirals with reduced/quenched star formation
have somewhat less disturbed morphologies than spirals with "normal"
star-formation activity, suggesting that these "passive" spirals have started
their morphological transformation into S0s. Visually identified mergers and
galaxies not identified as mergers but with similar roughness have similar
specific star formation rates and stellar ages. The degree of enhanced star
formation is thus linked to the degree of structural disturbance, regardless of
whether it is caused by major mergers or not. This suggests that merging
galaxies are not special in terms of their higher-than-normal star-formation
activity. Any physical process that produces "roughness", or regions of
enhanced luminosity density, will increase the star-formation activity in a
galaxy with similar efficiency. An alternative explanation is that star
formation episodes increase the galaxies' roughness similarly, regardless of
whether they are merger-induced or not.
