2017A&A...602A...5N

We make use of the deep Karl G. Jansky Very Large Array (VLA) COSMOS radio observations at 3GHz to infer radio luminosity functions of star-forming galaxies up to redshifts of z∼5 based on approximately 6000 detections with reliable optical counterparts. This is currently the largest radio-selected sample available out to z∼5 across an area of 2 square degrees with a sensitivity of rms ~=2.3 µJy/beam. By fixing the faint and bright end shape of the radio luminosity function to the local values, we find a strong redshift trend that can be fitted with a pure luminosity evolution L_1.4GHz∝(1 + z)^{(3.16±0.2)–(0.32±0.07)z}. We estimate star formation rates (SFRs) from our radio luminosities using an infrared (IR)-radio correlation that is redshift dependent. By integrating the parametric fits of the evolved luminosity function we calculate the cosmic SFR density (SFRD) history since z∼5. Our data suggest that the SFRD history peaks between 2<z<3 and that the ultraluminous infrared galaxies (100M_☉/yr<SFR<1000M_☉/yr) contribute up to ∼25% to the total SFRD in the same redshift range. Hyperluminous infrared galaxies (SFR>1000M_☉/yr) contribute an additional ≤2% in the entire observed redshift range. We find evidence of a potential underestimation of SFRD based on ultraviolet (UV) rest-frame observations of Lyman break galaxies at high redshifts (z≥4) on the order of 15-20%, owing to appreciable star formation in highly dust-obscured galaxies, which might remain undetected in such UV observations.