The brightest (and faintest) sources in the radio sky

TL;DR

This paper discusses the compilation and analysis of bright and faint radio sources in the sky, emphasizing their importance for understanding active galactic nuclei (AGN) and the advantages of radio observations over optical methods.

Contribution

It presents the GLEAM 4-Jy (G4Jy) sample of ~2,000 bright radio sources and integrates multi-frequency radio data with optical spectroscopy to improve AGN characterization.

Findings

Compilation of the G4Jy sample for southern sky radio sources.

Use of optical spectroscopy to derive redshifts for radio sources.

Insights into the origin of radio emission in faint sources.

Abstract

Radio observations allow us to identify a wide range of active galactic nuclei (AGN), which are galaxies that have gas accreting onto the supermassive black-hole at the centre. By observing these sources at multiple radio frequencies, a more-complete picture can be built of black-hole accretion activity. This completeness is aided by radio waves being unaffected by dust along the line-of-sight to these sources, which cannot be said for waves in the optical part of the electromagnetic spectrum. (Hence, dust obscuration leads to biases in AGN samples selected using optical observations.) A thorough compilation of ~2,000 of the brightest radio-sources in the southern sky [and so of particular relevance for the Square Kilometre Array (SKA) and its precursor/pathfinder telescopes] is the GLEAM 4-Jy (G4Jy) Sample, selected at 151 MHz, with subsets being followed up with MeerKAT and the Australia Telescope Compact Array (ATCA). Meanwhile, optical spectroscopy from the Southern African Large Telescope (SALT) is being used to derive crucial redshift information, both for G4Jy sources and for radio-faint AGN in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey. The origin of the radio emission in these faint sources is a subject of great debate within the AGN/radio-astronomy communities.