Prevalence of radio Active Galactic Nuclei in galaxy groups since z=3.5 in the COSMOS-Web field

Abstract

Radio active galactic nuclei (AGN) are key tracers of kinetic feedback from supermassive black holes. Although the dependence of their triggering on host stellar mass is well known, the impact of the large-scale environment across cosmic time is poorly understood. We investigate the role of the environment in triggering radio AGN activity, while also studying the dependence on stellar mass ($10\leq\log M_{\ast}\,{\rm [M_{\odot}]}\leq11.4$), radio luminosity ($22\leq\log L_{1.4}\,{\rm [W\,Hz^{-1}]}\leq26$), and redshift ($0.1\leq z \leq 3.5$). We combine the VLA-COSMOS 3 GHz Large Project with the COSMOS-Web galaxy and group catalogs, selecting radio-excess AGN and building radio luminosity functions (RLF) and radio AGN fractions separately for sources in galaxy groups (124 radio AGN) and in the field (405 radio AGN), out of the total of 20203 galaxies and 1678 galaxy groups. We fit the RLF to derive the cosmic evolution of radio AGN in different environments, and we provide a new parametric description of the radio AGN fractions as a function of environment, $M_{\ast}$, $L_{1.4}$, and z. Besides confirming the known positive correlation of radio AGN fraction with host $M_{\ast}$ in both groups and in the field, more importantly we find that the activation of a radio AGN in groups is enhanced relative to the field by a factor of 3--30 in space density and of 2 in radio AGN fraction at fixed stellar mass; the enhancement is also a function of $M_{\ast}$, $L_{1.4}$, and z. Furthermore, in all z bins, the radio AGN fractions peak within $r \leq 0.2R_{200}$. Overall, dense environments enhance radio AGN triggering out to at least z=3.5. We suggest the existence of a possible transition in the dominant triggering mechanism of radio AGN activity around z~1.5, potentially related to the intragroup medium in the core of groups at lower z and to merger and structure growth at earlier cosmic times.