The GLEAM 4-Jy (G4Jy) Sample: IV. Multiwavelength data and analysis

TL;DR

This paper updates the G4Jy radio source catalog with multiwavelength data, analyzes spectral curvature and radio properties, and explores host galaxy characteristics, providing new insights into radio galaxy evolution.

Contribution

It introduces a comprehensive multiwavelength dataset for the G4Jy catalog, including new host identifications, redshifts, and spectral analysis, and presents novel radio-power--size--age diagrams.

Findings

Radio spectral curvature (SCI) acts as a proxy for spectral age.

Radio-power--size--age diagram reveals candidate remnant and young radio sources.

G4Jy sources occupy the full WISE colour-colour space and host properties show no SCI relation.

Abstract

We provide an updated 'multiwavelength' version of the G4Jy catalogue (available at https://github.com/svw26/G4Jy, https://zenodo.org/communities/g4jy/records, and through VizieR), which has 127 new host-galaxy identifications, as described in Paper III of this paper series. We also supplement the redshift information (0.0 < z < 3.6), gathered in Paper III, with $griz$ photometry available through DR10 of the DESI Legacy Surveys. Together, this legacy dataset allows us to investigate the multiwavelength properties of these southern radio-bright galaxies, which includes an initial analysis of radio spectral-curvature for this complete sample (S_151MHz > 4 Jy). For example, we present (for the first time in the literature) the radio-power--size diagram as a function of radio spectral-curvature, [P--D](SCI), noting that the spectral-curvature index (SCI) can act as a proxy for the spectral age of the radio source. This radio-power--size--age diagram shows a predominance of radio galaxies with SCI > 0.15 and D < 200 kpc, which are candidates for both remnant radio-galaxies and young radio sources, and a vast range of linear sizes for candidate restarted radio-galaxies (having SCI < -0.15). We also show that (i) G4Jy sources populate the entirety of WISE colour-colour space, (ii) optically point-like sources (i.e. candidate quasars) are brighter than the well-studied K--z relation (as expected), and (iii) there is no relation between the SCI of the radio source and its host-galaxy properties.