Galaxy And Mass Assembly (GAMA): The 325 MHz Radio Luminosity Function
  of AGN and Star Forming Galaxies
  Measurement of the evolution of both active galactic nuclei (AGN) and
star-formation in galaxies underpins our understanding of galaxy evolution over
cosmic time. Radio continuum observations can provide key information on these
two processes, in particular via the mechanical feedback produced by radio jets
in AGN, and via an unbiased dust-independent measurement of star-formation
rates. In this paper we determine radio luminosity functions at 325 MHz for a
sample of AGN and star-forming galaxies by matching a 138 deg sq. radio survey
conducted with the Giant Metrewave Radio Telescope (GMRT), with optical imaging
and redshifts from the Galaxy And Mass Assembly (GAMA) survey. We find that the
radio luminosity function at 325 MHz for star-forming galaxies closely follows
that measured at 1.4 GHz. By fitting the AGN radio luminosity function out to
$z = 0.5$ as a double power law, and parametrizing the evolution as ${\Phi}
\propto (1 + z)^{k}$ , we find evolution parameters of $k = 0.92 \pm 0.95$
assuming pure density evolution and $k = 2.13 \pm 1.96$ assuming pure
luminosity evolution. We find that the Low Excitation Radio Galaxies are the
dominant population in space density at lower luminosities. Comparing our 325
MHz observations with radio continuum imaging at 1.4 GHz, we determine separate
radio luminosity functions for steep and flat-spectrum AGN, and show that the
beamed population of flat-spectrum sources in our sample can be shifted in
number density and luminosity to coincide with the unbeamed population of
steep-spectrum sources, as is expected in the orientation based unification of
AGN.
