Eliab Malefahlo | Searcharxiv

arXiv2026

MIGHTEE: The evolving radio luminosity functions of star-forming galaxies to $z\sim 4.5$ and the cosmic history of star formation

A key question in extragalactic astronomy is how the star-formation rate density (SFRD) evolves over cosmic time. A powerful way of addressing this question is using radio-continuum observations, where the radio waves are unaffected by dust and are able to reach sufficient resolution to resolve individual galaxies. We present an investigation of the 1.4 GHz radio luminosity functions (RLFs) of star-forming galaxies (SFGs) and Active Galactic Nuclei (AGN) using deep radio continuum observations in the COSMOS and XMM-LSS fields, covering a combined area of $\sim 4\,\mathrm{deg}^2$. These data enable the most accurate measurement of the evolution in the SFRD from mid-frequency radio continuum observations. We model the total RLF as the sum of evolving SFG and AGN components, negating the need for individual source classification. We find that the SFGs have systematically higher space densities at fixed luminosity than found in previous radio studies, but consistent with more recent studies with MeerKAT. We attribute this to the excellent low-surface brightness sensitivity of MeerKAT. We then determine the evolution of the SFRD. Adopting the far-infrared - radio correlation results in a significantly higher the SFRD at $z > 1$, compared to combined UV and far-infrared measurements. However, using more recent relations for the correlation between star-formation rate and radio luminosity, based on full spectral energy distribution modelling, can resolve this apparent discrepancy. Thus radio observations provide a powerful method of determining the total SFRD, in the absence of dust-sensitive far-infrared data.

astro-ph.GA↗

arXiv2020

The optically-selected 1.4-GHz quasar luminosity function below 1 mJy

We present the radio luminosity function (RLF) of optically-selected quasars below 1~mJy, constructed by applying a Bayesian-fitting stacking technique to objects well below the nominal radio flux-density limit. We test the technique using simulated data, confirming that we can reconstruct the RLF over three orders of magnitude below the typical $5σ$ detection threshold. We apply our method to 1.4-GHz flux-densities from the Faint Images of the Radio Sky at Twenty-cm survey (FIRST), extracted at the positions of optical quasars from the Sloan Digital Sky Survey (SDSS) over seven redshift bins up to $z=2.15$ {and measure the RLF down to two orders of magnitude below the FIRST detection threshold}. In the lowest redshift bin ($0.2<z<0.45$), we find that our measured RLF agrees well with deeper data from the literature. The RLF for the radio-loud quasars flattens below $\log_{10}[L_{1.4}/{\rm W\,Hz}^{-1}] \approx 25.5$ and becomes steeper again below $\log_{10}[L_{1.4}/{\rm W\,Hz}^{-1}] \approx 24.8$, where radio-quiet quasars start to emerge. The radio luminosity where radio-quiet quasars emerge coincides with the luminosity where star-forming galaxies are expected to start to dominate the radio source counts. This implies that there could be a significant contribution from star formation in the host galaxies, but additional data is required to investigate this further. The higher-redshift bins show a similar behaviour as for the lowest-$z$ bin, implying that the same physical process may be responsible.

astro-ph.GA↗