The Relationship Between Star-formation Activity and Galaxy Structural
  Properties in CANDELS and a Semi-analytic Model
  We study the correlation of galaxy structural properties with their location
relative to the SFR-M* correlation, also known as the star formation "main
sequence" (SFMS), in the CANDELS and GAMA surveys and in a semi-analytic model
(SAM) of galaxy formation. We first study the distribution of median Sersic
index, effective radius, star formation rate (SFR) density and stellar mass
density in the SFR-M* plane. We then define a redshift dependent main sequence
and examine the medians of these quantities as a function of distance from this
main sequence, both above (higher SFRs) and below (lower SFRs). Finally, we
examine the distributions of distance from the main sequence in bins of these
quantities. We find strong correlations between all of these galaxy structural
properties and the distance from the SFMS, such that as we move from galaxies
above the SFMS to those below it, we see a nearly monotonic trend towards
higher median Sersic index, smaller radius, lower SFR density, and higher
stellar density. In the semi-analytic model, bulge growth is driven by mergers
and disk instabilities, and is accompanied by the growth of a supermassive
black hole which can regulate or quench star formation via Active Galactic
Nucleus (AGN) feedback. We find that our model qualitatively reproduces the
trends described above, supporting a picture in which black holes and bulges
co-evolve, and AGN feedback plays a critical role in moving galaxies off of the
SFMS.
