Radio AGN as beacons of galaxy overdensities up to z~4

Radio AGN are key tracers of BH growth and feedback, yet the role of environment across cosmic time in regulating their incidence is poorly constrained. While there is a strong correspondence between radio AGN and massive galaxies in overdense regions in the local Universe, it is still unclear if the same picture holds at high-z. In this talk, I will present our ongoing investigation on how the environment, the stellar mass, and redshift shape the occurrence of radio AGN. We exploit the incredibly rich dataset available for the COSMOS field, including the COSMOS-Web coverage with NIRCam, the deep VLA 3 GHz radio AGN catalog, and a recently released catalog of >1500 galaxy groups up to z~4. We measure the radio AGN luminosity function separately for galaxies in groups and in the field, quantifying environmental enhancement of AGN density as a function of radio power, stellar mass, and redshift. By modeling these trends, and by comparing the AGN fractions between group and field galaxies in bins of stellar mass, we disentangle the relative contributions of host galaxy mass, environment, and cosmic epoch to the triggering of radio AGN activity. Our findings suggest that large-scale (Mpc) overdensities can significantly enhance the incidence of radio AGN jets since z~4, at fixed galaxy stellar mass. These results pinpoint the primary role played by dense environments in fueling black hole growth from the local galaxy groups to the high redshift proto-groups and proto-clusters.