The Nature of the Faint Low-Frequency Radio Source Population
  We present a multi-wavelength study into the nature of faint radio sources in
a deep radio image with the Giant Meterwave Radio Telescope at 612\,MHz
covering 1.2 deg$^2$ of the ELAIS N1 region. We detect 2800 sources above
50~$\mu$Jy\,beam$^{-1}$. By matching to multi-wavelength data we obtain a
redshift estimate for 63\%, with 29\% based on spectroscopy. For 1526 of the
sources with redshifts we use radio and X-ray luminosity, optical spectroscopy,
mid-infrared colors, and 24$\mu$m and IR to radio flux ratios to search for the
presence of an AGN. The analysis reveals a rapid change in the population as
flux density decreases from $\sim$500\,$\mu$Jy to $\sim$100\,$\mu$Jy. We find
that 80.3\% of the objects show no evidence of AGN and have multi-wavelength
properties consistent with radio emission from star forming galaxies (SFG). We
classify 11.4\% as Radio Quiet (RQ) AGN and the remaining 8.3\% as Radio Loud
(RL) AGN.
  The redshift of all populations extends to $z > 3$ with a median of $\sim$1.
The median radio and far-IR luminosity increases systematically from SFG, to RQ
AGN and RL AGN. The median $q_{\rm 24 \mu m}$ for SFG, $0.89\pm0.01$ is
slightly below that for RQ AGN, $1.05\pm0.03$, and both differ substantially
from the value for RL AGN of $-0.06\pm0.07$. However, SFG and RQ AGN show no
significant difference in far-IR/radio ratios and have statistically
indistinguishable star formation rates inferred from radio and far-IR
luminosities. We conclude that radio emission from host galaxies of RQ AGN in
this flux density regime result primarily from star formation activity.
