Why z > 1 radio - loud galaxies are commonly located in proto - clusters

Distant powerful radio-loud active galactic nuclei (RLAGN) tend to reside in dense environments and are commonly found in proto-clusters at z > 1.3. We examine whether this occurs because RLAGN are hosted by massive galaxies which preferentially reside in rich environments. We compare the environments of powerful RLAGN at 1.3 < z < 3.2 from the CARLA survey to a sample of radio-quiet galaxies matched in mass and redshift. We find the environments of RLAGN are significantly denser than those of radio-quiet galaxies, implying that not more than 50% of massive galaxies in this epoch can host powerful radio-loud jets. This is not an observational selection effect as we find no evidence to suggest it is easier to observe the radio emission when the galaxy resides in a dense environment. We therefore suggest that the dense Mpc-scale environment fosters the formation of a radio-jet from an AGN. We show that the number density of potential RLAGN host galaxies is consistent with every > 1014 M⊙ cluster having experienced powerful radio-loud feedback of duration ∼60 Myr during 1.3 < z < 3.2. This feedback could heat the intracluster medium to the extent of 0.51 keV per gas particle, which could limit the amount of gas available for further star formation in the proto-cluster galaxies.