The VLA-COSMOS 3 GHz Large Project: Star formation properties and radio
  luminosity functions of AGN with moderate-to-high radiative luminosities out
  to $z\sim6$
  We study a sample of 1,604 moderate-to-high radiative luminosity active
galactic nuclei (HLAGN) selected at 3 GHz within the VLA-COSMOS 3 GHz Large
Project. These were classified by combining multiple AGN diagnostics: X-ray
data, mid-infrared data and broad-band spectral energy distribution fitting. We
decompose the total radio 1.4 GHz luminosity ($\mathrm{L_{1.4\ GHz,TOT}}$) into
the emission originating from star formation and AGN activity by measuring the
excess in $\mathrm{L_{1.4\ GHz,TOT}}$ relative to the infrared-radio
correlation of star-forming galaxies. To quantify the excess, for each source
we calculate the AGN fraction ($\mathrm{f_{AGN}}$), the fractional contribution
of AGN activity to $\mathrm{L_{1.4\ GHz,TOT}}$. The majority of the HLAGN,
$(68.0\pm1.5)\%$, are dominated by star-forming processes ($f_{AGN}\leq0.5$),
while $(32.0\pm1.5)\%$ are dominated by AGN-related radio emission
($0.5<f_{AGN}\leq1$). We use the AGN-related 1.4 GHz emission to derive the 1.4
GHz AGN luminosity functions of HLAGN. By assuming pure density and pure
luminosity evolution models we constrain their cosmic evolution out to
$z\sim6$, finding $\mathrm{\Phi^* (z) \propto
(1+z)^{(2.64\pm0.10)+(-0.61\pm0.04) z}}$ and $\mathrm{L^* (z) \propto
(1+z)^{(3.97\pm0.15) + (-0.92\pm0.06)z}}$. These evolutionary laws show that
the number and luminosity density of HLAGN increased from higher redshifts
($z\sim6$) up to a maximum in the redshift range $ 1<z<2.5$, followed by a
decline towards local values. By scaling the 1.4 GHz AGN luminosity to kinetic
luminosity using the standard conversion, we estimate the kinetic luminosity
density as a function of redshift. We compare our result to the semi-analytic
models of radio mode feedback finding that this feedback could have played an
important role in the context of AGN-host coevolution in HLAGN which show
evidence of AGN-related radio emission ($f_{AGN}>0$).
