We explore the cosmic evolution of radio AGN with low radio powers ( \mathrm { L } _ { \mathrm { 1.4 GHz } } Â \lesssim 5 \times 10 ^ { 25 } Â WÂ Hz ^ { -1 } ) out to z = 1.3 using to-date the largest sample of \sim 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 \pm 0.1 } , and \Phi _ { * } \propto ( 1 + z ) ^ { 1.1 \pm 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 ( \mathrm { L } _ { \mathrm { 1.4 GHz } } Â > 5 \times 10 ^ { 25 } Â WÂ Hz ^ { -1 } ) radio AGN over the same cosmic time interval , constrained using the 3CRR , 6CE , and 7CRS radio surveys by Willott et al .
( 97 ) .
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 \sim 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 .