2025MNRAS.541.3636W

In this work, we study a robust, $K_{s}$-band complete, spectroscopically confirmed sample of 104 unobscured (Type-1) quasars within the COSMOS and XMM-LSS fields of the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, at $0.60 < z_{\mathrm{spec}} < 3.41$. The quasars are selected via $gJK_{s}$ colour-space and, with 1.3-GHz flux-densities reaching rms $\approx$ 3.0 $\mu$Jy beam$^{-1}$, we find a radio-loudness fraction of 5 per cent. Thanks to the deep, multiwavelength data sets that are available over these fields, the properties of radio-loud and radio-quiet quasars can be studied in a statistically robust way, with the emphasis of this work being on the active-galactic-nuclei (AGNs)-related and star-formation-related contributions to the total radio emission. We employ multiple star-formation-rate estimates for the analysis so that our results can be compared more easily with others in the literature, and find that the fraction of sources that have their radio emission dominated by the AGN crucially depends on the SFR estimate that is derived from the radio luminosity. When redshift dependence is not taken into account, a larger fraction of sources is classed as having their radio emission dominated by the AGN. When redshift dependence is considered, a larger fraction of our sample is tentatively classed as 'starbursts'. We also find that the fraction of (possible) starbursts increases with redshift, and provide multiple suggestions for this trend.