A deep radio view of the evolution of the cosmic star-formation rate density from a stellar-mass selected sample in VLA-COSMOS
We present the 1.4 GHz radio luminosity functions (RLFs) of galaxies in the COSMOS field, measured above and below the 5σ detection threshold, using a Bayesian model-fitting technique. The radio flux-densities from VLA-COSMOS 3-GHz data, are extracted at the position of stellar mass-selected galaxies. We fit a local RLF model, which is a combination of active galactic nuclei (AGN) and star-forming galaxies (SFG), in 10 redshift bins with a pure luminosity evolution (PLE) model. Our RLF exceeds previous determinations at low-radio luminosities at z < 1.6 with the same radio data, due to our ability to directly constrain the knee and faint-end slope of the RLF. Beyond z ∼ 2, we find that the SFG part of the RLF exhibits a negative evolution (L* moves to lower luminosities) due to the decrease in low stellar-mass galaxies in our sample at high redshifts. From the RLF for SFGs, we determine the evolution in the cosmic star-formation-rate density (SFRD), which we find to be consistent with the established behaviour up to z ∼ 1 using far-infrared data, but exceeds that from the previous radio-based work for the reasons highlighted above. Beyond z ∼ 1.5 the cosmic SFRD declines. We note that the relation between radio luminosity and SFR is crucial in measuring the cosmic SFRD from radio data at z > 1.5. We investigate the effects of stellar mass on the total RLF by splitting our sample into low (108.5 ≤ M/M⊙ ≤ 1010) and high (M > 1010 M⊙) stellar-mass subsets. We find that the SFRD is dominated by sources in the high stellar masses bin, at all redshifts.