COLA III. Radio Detection of AGN in Compact Moderate Luminosity
  Infra-Red Galaxies
  We present results from 4.8 GHz VLA and Global-VLBI observations of the
northern half of the moderate FIR luminosity (median L_IR = 10^11.01 L_Sol)
COLA sample of star-forming galaxies. VLBI sources are detected in a high
fraction (20/90) of the galaxies observed. The radio luminosities of these
cores (~10^21 W/Hz) are too large to be explained by radio supernovae or
supernova remnants and we argue that they are instead powered by AGN. These
sub-parsec scale radio cores are preferentially detected toward galaxies whose
VLA maps show bright 100-500 parsec scale nuclear radio components. Since these
latter structures tightly follow the FIR to radio-continuum correlation for
star-formation we conclude that the AGN powered VLBI sources are associated
with compact nuclear starburst environments. The implications for possible
starburst-AGN connections are discussed. The detected VLBI sources have a
relatively narrow range of radio luminosity consistent with models in which
intense compact Eddington-limited starbursts regulate the gas supply onto a
central super-massive black hole. The high incidence of AGN radio cores in
compact starbursts suggests little or no delay between the starburst phase and
the onset of AGN activity.
