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

ABSTRACT We provide an updated ‘multiwavelength’ version of the G4Jy catalogue that has 127 new host-galaxy identifications, as described in Paper III of this paper series. We also supplement the redshift information ($0.0 \lt z \lt 3.6$), gathered in Paper III, with $griz$ photometry available through DR10 of the DESI Legacy Surveys. Together, this legacy data set 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 ($S_{\mathrm{151\, MHz}}\gt 4$ 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 $\gt 0.15$ and $D\lt 200$ 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 $\lt -0.15$). 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.