The host galaxies of micro-Jansky radio sources
  We combine a deep 0.5~deg$^2$, 1.4~GHz deep radio survey in the Lockman Hole
with infrared and optical data in the same field, including the SERVS and
UKIDSS near-infrared surveys, to make the largest study to date of the host
galaxies of radio sources with typical radio flux densities $\sim 50 \;\mu$Jy.
87% (1274/1467) of radio sources have identifications in SERVS to $AB\approx
23.1$ at 3.6 or 4.5$\mu$m, and 9% are blended with bright objects (mostly
stars), leaving only 4% (59 objects) which are too faint to confidently
identify in the near-infrared. We are able to estimate photometric redshifts
for 68% of the radio sources. We use mid-infrared diagnostics to show that the
source population consists of a mixture of star forming galaxies, rapidly
accreting (cold mode) AGN and low accretion rate, hot mode AGN, with neither
AGN nor starforming galaxies clearly dominating. We see the breakdown in the
$K-z$ relation in faint radio source samples, and show that it is due to radio
source populations becoming dominated by sources with radio luminosities $\sim
10^{23}\;{\rm WHz^{-1}}$. At these luminosities, both the star forming galaxies
and the cold mode AGN have hosts with stellar luminosities about a factor of
two lower than those of hot mode AGN, which continue to reside in only the most
massive hosts. We show that out to at least $z\sim 2$, galaxies with stellar
masses $>10^{11.5}\, M_{\odot}$ have a radio-loud fraction up to $\sim 30$%.
This is consistent with there being a sufficient number of radio sources that
radio-mode feedback could play a role in galaxy evolution.
