The VLA-COSMOS 3 GHz Large Project: Cosmic evolution of radio AGN and implications for radio-mode feedback since z ~ 5

¹ Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000 Zagreb, Croatia
e-mail: vs@phy.hr
² Istituto di Radioastronomia di Bologna – INAF, via P. Gobetti, 101, 40129 Bologna, Italy
³ Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
⁴ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ Argelander Institut for Astronomy, Auf dem Hügel 71, 53121 Bonn, Germany
⁷ INAF–Osservatorio Astronomico di Bologna, via Piero Gobetti 93/3, 40129 Bologna, Italy

Received: 23 February 2017
Accepted: 10 May 2017

Abstract

Based on a sample of over 1800 radio AGN at redshifts out to z ~ 5, which have typical stellar masses within ~3 × (10¹⁰ − 10¹¹)M_⊙, and 3 GHz radio data in the COSMOS field, we derived the 1.4 GHz radio luminosity functions for radio AGN (L_{1.4 GHz}~ 10²² − 10²⁷ W Hz^-1) 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 Φ^∗ ∝ (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.