The VLA-COSMOS 3~GHz Large Project: Cosmic evolution of radio AGN and
  implications for radio-mode feedback since z~5
  Based on a sample of over 1,800 radio AGN at redshifts out to z~5, which have
typical stellar masses within ~3x(10^{10}-10^{11}) Msol, and 3 GHz radio data
in the COSMOS field, we derived the 1.4 GHz radio luminosity functions for
radio AGN (L_1.4GHz ~ 10^{22}-10^{27} W/Hz) out to z~5. We constrained the
evolution of this population via continuous models of pure density and pure
luminosity evolutions, and we found best-fit parametrizations of
Phi*~(1+z)^{(2.00+/-0.18)-(0.60+/-0.14)z}, and
L*~(1+z)^{(2.88+/-0.82)-(0.84+/-0.34)z}, respectively, with a turnover in
number and luminosity densities of the population at z~1.5. We converted 1.4
GHz luminosity to kinetic luminosity taking uncertainties of the scaling
relation used into account. We thereby derived the cosmic evolution of the
kinetic luminosity density provided by the AGN and compared this luminosity
density to the radio-mode AGN feedback assumed in the Semi-Analytic Galaxy
Evolution (SAGE) model, i.e., to the redshift evolution of the central
supermassive black hole accretion luminosity taken in the model as the source
of heating that offsets the energy losses of the cooling, hot halo gas, and
thereby limits further stellar mass growth of massive galaxies. We find that
the kinetic luminosity exerted by our radio AGN may be high enough to balance
the radiative cooling of the hot gas at each cosmic epoch since z~5. However,
although our findings support the idea of radio-mode AGN feedback as a
cosmologically relevant process in massive galaxy formation, many
simplifications in both the observational and semi-analytic approaches still
remain and need to be resolved before robust conclusions can be reached.
