Radio-AGN Feedback: When the Little Ones were Monsters
  We present a study of the evolution of the fraction of radio-loud active
galactic nuclei (AGN) as a function of their host stellar mass. We make use of
two samples of radio galaxies: one in the local universe, $0.01 < z < 0.3$,
using a combined SDSS-NVSS sample and one at higher redshifts, $0.5 < z < 2$,
constructed from the VLA-COSMOS_DEEP Radio Survey at 1.4 GHz and a
K$_s$-selected catalogue of the COSMOS/UltraVISTA field. We observe an increase
of more than an order of magnitude in the fraction of lower mass galaxies ($M_*
< 10^{10.75}$ M$_{\odot}$) which host Radio-Loud AGN with radio powers
$P_{1.4GHz} > 10^{24}$ W/Hz at z ~ 1-2 while the radio-loud fraction for higher
mass galaxies ($M_* > 10^{11.25}$ M$_{\odot}$) remains the same. We argue that
this increase is driven largely by the increase in cold or radiative mode
accretion with increasing cold gas supply at earlier epochs. The increasing
population of low mass Radio-Loud AGN can thus explain the upturn in the Radio
Luminosity Function (RLF) at high redshift which is important for understanding
the impact of AGN feedback in galaxy evolution.
