Cosmic evolution of radio selected active galactic nuclei in the COSMOS field

Details Cosmic evolution of radio selected active galactic nuclei in the COSMOS field Cosmic evolution of radio selected active galactic nuclei in the COSMOS field

2009-01-21

arxiv.org/abs/0901.3372v1

Astrophys.J.696:24-39,2009; Erratum-ibid.708:909,2010

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

18 pages, 14 figures, to appear in ApJ

Scientific paper

10.1088/0004-637X/696/1/24 10.10

We explore the cosmic evolution of radio AGN with low radio powers (L_1.4GHz < 5\times10^25 W/Hz) out to z=1.3 using to-date the largest sample of ~600 low luminosity radio AGN at intermediate redshift drawn from the VLA-COSMOS survey. We derive the radio luminosity function for these AGN, and its evolution with cosmic time assuming two extreme cases: i) pure luminosity and ii) pure density evolution. The former and latter yield L_*\propto(1+z)^(0.8+/-0.1), and Phi*\propto (1+z)^(1.1+/-0.1), respectively, both implying a fairly modest change in properties of low radio-power AGN since z=1.3. We show that this is in stark contrast with the evolution of powerful (L_1.4GHz > 5\times10^25 W/Hz) radio AGN over the same cosmic time interval, constrained using the 3CRR, 6CE, and 7CRS radio surveys by Willott et al. (2001). We demonstrate that this can be explained through differences in black hole fueling and triggering mechanisms, and a dichotomy in host galaxy properties of weak and powerful AGN. Our findings suggest that high and low radio-power AGN activity is triggered in different stages during the formation of massive red galaxies. We show that weak radio AGN occur in the most massive galaxies already at z~1, and they may significantly contribute to the heating of their surrounding medium and thus inhibit gas accretion onto their host galaxies, as recently suggested for the `radio mode' in cosmological models.

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