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 (S151 MHz 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.
White et al. (Thu,) studied this question.