2018A&A...620A.192C

We have studied a sample of 1604 moderate-to-high radiative luminosity active galactic nuclei (HLAGN) selected at 3GHz within the VLA-COSMOS 3GHz Large Project. These were classified by combining multiple AGN diagnostics: X-ray data, mid-infrared data and broadband spectral energy distribution fitting. We decomposed the total radio 1.4GHz luminosity (L_1.4GHz,TOT) into the emission originating from star formation and AGN activity by measuring the excess in L_1.4GHz,TOT relative to the infrared-radio correlation of star-forming galaxies. To quantify the excess, for each source we calculated the AGN fraction (f_AGN) defined as the fractional contribution of AGN activity to L_1.4GHz,TOT. The majority of the HLAGN, (68.0±1.5)%, are dominated by star-forming processes (f_AGN≤0.5), while (32.0±1.5)% are dominated by AGN-related radio emission (0.5<f_AGN≤1). We used the AGN-related 1.4GHz emission to derive the 1.4GHz AGN luminosity functions of HLAGN. By assuming pure density and pure luminosity evolution models we constrained their cosmic evolution out to z∼6, finding Φ^*(z)∝(1+z)^{(2.64±0.10)+(–0.61±0.04)z} and L^*(z)∝(1+z)^{(3.97±0.15)+(–0.92±0.06)z}. These evolutionary laws show that the number and luminosity density of HLAGN increased from higher redshifts (z∼6) up to a maximum in the redshift range 1<z<2.5, followed by a decline toward local values. By scaling the 1.4GHz AGN luminosity to kinetic luminosity using the standard conversion, we estimate the kinetic luminosity density as a function of redshift. We compare our result to the semi-analytic models of radio mode feedback, and find that this feedback could have played an important role in the context of AGN-host co-evolution in HLAGN which shows evidence of AGN-related radio emission (f_AGN>0).