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

TL;DR

This study uses deep 1.4 GHz radio observations to accurately measure the evolution of star-forming galaxies' luminosity functions and the cosmic star formation rate density up to redshift 4.5, highlighting the effectiveness of radio data.

Contribution

It models the radio luminosity functions of star-forming galaxies and AGN without source classification, providing new insights into star formation history using radio data.

Findings

Star-forming galaxies have higher space densities than previously reported.

Radio-based SFRD estimates are higher at z > 1 when using FIR-radio correlation.

Full spectral energy distribution modeling can reconcile radio and IR-based SFRD measurements.

Abstract

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.