The GLEAM 200 MHz Local Radio Luminosity Function for AGN and
  Star-forming Galaxies
  The GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) is a
radio continuum survey at 76-227 MHz of the entire southern sky (Declination
$<+30\deg$) with an angular resolution of $\approx 2$ arcmin. In this paper, we
combine GLEAM data with optical spectroscopy from the 6dF Galaxy Survey to
construct a sample of 1,590 local (median $z \approx 0.064$) radio sources with
$S_{200\,\mathrm{MHz}} > 55$ mJy across an area of $\approx
16,700~\mathrm{deg}^{2}$. From the optical spectra, we identify the dominant
physical process responsible for the radio emission from each galaxy: 73 per
cent are fuelled by an active galactic nucleus (AGN) and 27 per cent by star
formation. We present the local radio luminosity function for AGN and
star-forming galaxies at 200 MHz and characterise the typical radio spectra of
these two populations between 76 MHz and $\sim 1$ GHz. For the AGN, the median
spectral index between 200 MHz and $\sim 1$ GHz, $\alpha_{\mathrm{high}}$, is
$-0.600 \pm 0.010$ (where $S \propto \nu^{\alpha}$) and the median spectral
index within the GLEAM band, $\alpha_{\mathrm{low}}$, is $-0.704 \pm 0.011$.
For the star-forming galaxies, the median value of $\alpha_{\mathrm{high}}$ is
$-0.650 \pm 0.010$ and the median value of $\alpha_{\mathrm{low}}$ is $-0.596
\pm 0.015$. Among the AGN population, flat-spectrum sources are more common at
lower radio luminosity, suggesting the existence of a significant population of
weak radio AGN that remain core-dominated even at low frequencies. However,
around 4 per cent of local radio AGN have ultra-steep radio spectra at low
frequencies ($\alpha_{\mathrm{low}} < -1.2$). These ultra-steep-spectrum
sources span a wide range in radio luminosity, and further work is needed to
clarify their nature.
