The GLEAM 4-Jy (G4Jy) Sample: V. Broadband spectral analysis

The G4Jy Sample consists of 1,863 of the brightest sources in the southern sky, as selected at 151 MHz using the GaLactic and Extragalactic All-sky MWA (GLEAM) survey. We supplement existing, low-frequency radio data by completing visual inspection of radio images from the Rapid ASKAP Continuum Survey (RACS) at 887.5, 1367.5 and 1655.5 MHz. Doing so on a source-by-source basis allows us to assess the quality of the association of the radio emission, which we indicate via a flag system. Having multiple radio flux-densities allows us to construct broadband radio spectral energy distributions (SEDs), and these extend up to 20 GHz for sources that also have data from the Australia Telescope Compact Array (ATCA). We fit polynomial functions to these SEDs, and determine the distribution of sources that are best-fit by absorption models, these accounting for 11 per cent of the sample. The SEDs are further modelled using the Radio AGN in Semi-analytic Environments (RAiSE) framework, for three assumed density-profiles (set by typical halo masses of 10 12.5, 10 13.5, and 10 14.5 Msol). The derived source ages show the expected distribution in the radio-power--size (P--D) diagram, whilst derived jet powers show non-linear behaviour. The latter is believed to be the result of higher densities, associated with higher magnetic fields, restricting the expansion of the radio jets/lobes.