The GLEAM 200 MHz Local Radio Luminosity Function for AGN and Star-forming Galaxies

Abstract

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 $<+30°$) 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.

28 pages, 18 figures, accepted for publication in PASA

References in corpus (13)

• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• An Objective Definition for the Main Sequence of Star-Forming Galaxies
• Radio sources in the 6dFGS: Local luminosity functions at 1.4 GHz for star-forming galaxies and radio-loud AGN
• Color--Mass-to-Light Ratio Relations for Disk Galaxies
• Revisiting the Fanaroff-Riley dichotomy and radio-galaxy morphology with the LOFAR Two-Metre Sky Survey (LoTSS)
• Stellar mass estimates in early-type galaxies: procedures, uncertainties and models dependence
• The main sequence of star forming galaxies I. The local relation and its bending
• A radio spectral index map and catalogue at 147-1400 MHz covering 80 per cent of the sky
• Remnant radio-loud AGN in the Herschel-ATLAS field
• The ATESP 5 GHz radio survey I. Source counts and spectral index properties of the faint radio population
• Radio Sources in the Nearby Universe
• Cosmic evolution of star-forming galaxies to $z\simeq 1.8$ in the faint low-frequency radio source population
• GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey III: South Galactic Pole data release

Cited by in corpus (2)

• Cosmic evolution of radio-excess AGNs in quiescent and star-forming galaxies across $0<z<4$
• The GLEAM 4-Jy (G4Jy) Sample: IV. Multiwavelength data and analysis