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 ) with an angular resolution of 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 ) radio sources with mJy across an area of . From the optical spectra, we identify the dominant physical process responsible for the radio emission from each galaxy: 73% are fuelled by an active galactic nucleus (AGN) and 27% by star formation. We present the local radio luminosity function for AGN and star-forming (SF) galaxies at 200 MHz and characterise the typical radio spectra of these two populations between 76 MHz and GHz. For the AGN, the median spectral index between 200 MHz and GHz, , is (where ) and the median spectral index within the GLEAM band, , is . For the SF galaxies, the median value of is and the median value of is . 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% of local radio AGN have ultra-steep radio spectra at low frequencies ( ). These ultra-steep-spectrum sources span a wide range in radio luminosity, and further work is needed to clarify their nature.