The evolving relations between size, mass, surface density, and star
  formation in 3x10^4 galaxies since z=2
  The presence of massive, compact, quiescent galaxies at z>2 presents a major
challenge for theoretical models of galaxy formation and evolution. Using one
of the deepest large public near-IR surveys to date, we investigate in detail
the correlations between star formation and galaxy structural parameters (size,
stellar mass, and surface density) from z=2 to the present. At all redshifts,
massive quiescent galaxies (i.e. those with little or no star formation) occupy
the extreme high end of the surface density distribution and follow a tight
mass-size correlation, while star-forming galaxies show a broad range of both
densities and sizes. Conversely, galaxies with the highest surface densities
comprise a nearly-homogeneous population with little or no ongoing star
formation, while less dense galaxies exhibit high star-formation rates and
varying levels of dust obscuration. Both the sizes and surface densities of
quiescent galaxies evolve strongly from z=2-0; we parameterize this evolution
for both populations with simple power law functions and present best-fit
parameters for comparison to future theoretical models. Higher-mass quiescent
galaxies undergo faster structural evolution, consistent with previous results.
Interestingly, star-forming galaxies' sizes and densities evolve at rates
similar to those of quiescent galaxies. It is therefore possible that the same
physical processes drive the structural evolution of both populations,
suggesting that "dry mergers" may not be the sole culprit in this size
evolution.
