Massive Compact Galaxies with High-Velocity Outflows: Morphological
  Analysis and Constraints on AGN Activity
  We investigate the process of rapid star formation quenching in a sample of
12 massive galaxies at intermediate redshift (z~0.6) that host high-velocity
ionized gas outflows (v>1000 km/s). We conclude that these fast outflows are
most likely driven by feedback from star formation rather than active galactic
nuclei (AGN). We use multiwavelength survey and targeted observations of the
galaxies to assess their star formation, AGN activity, and morphology. Common
attributes include diffuse tidal features indicative of recent mergers
accompanied by bright, unresolved cores with effective radii less than a few
hundred parsecs. The galaxies are extraordinarily compact for their stellar
mass, even when compared with galaxies at z~2-3. For 9/12 galaxies, we rule out
an AGN contribution to the nuclear light and hypothesize that the unresolved
core comes from a compact central starburst triggered by the dissipative
collapse of very gas-rich progenitor merging disks. We find evidence of AGN
activity in half the sample but we argue that it accounts for only a small
fraction (<10%) of the total bolometric luminosity. We find no correlation
between AGN activity and outflow velocity and we conclude that the fast
outflows in our galaxies are not powered by on-going AGN activity, but rather
by recent, extremely compact starbursts.
