The Contribution of Active Galactic Nuclei to the Microjansky Radio
  Population
  A X-ray background synthesis model is used to calculate the contribution of
Active Galactic Nuclei (AGNs) to the 1.4 GHz number counts between 100 nJy and
10 mJy. The number counts are broken down into contributions from radio-quiet
and radio-loud AGNs, obscured and unobscured AGNs, and for different ranges in
redshift and 2-10 keV X-ray luminosity, L_X. Compton-thick AGNs are included,
but only to the level required to fit the peak of the X-ray background. The
predicted radio counts show that the microJy AGN population will be dominated
by obscured, radio-quiet Seyfert galaxies with log L_X < 43, and spanning 0 < z
<~ 3. However, depending on the exact relationship between the radio and X-ray
luminosities in radio-quiet AGNs, additional radio flux due to star-formation
within AGN host galaxies may be necessary in order to match the observed AGN
counts at a flux density of ~50 microJy. The star-formation rates (SFR)
required are modest, only ~3 Msun per year, assuming a constant rate with z and
L_X. A more observationally and theoretically motivated relationship, where the
SFR \propto (1+z)^{1.76}(log L_X-40)^{3.5}, will also account for the observed
counts. The microJy AGN population will provide a very clean sample to trace
the accretion and galactic star-formation histories of Seyfert galaxies over a
significant fraction of cosmic time.
