Active galactic nucleus activity in brightest cluster galaxies at intermediate redshifts in Sunyaev-Zel’dovich--selected clusters
Abstract
Brightest cluster galaxies (BCGs) host some of the most powerful active galactic nuclei (AGNs) and play a central role in regulating the heating--cooling balance of the intracluster medium. While radio-mode feedback is well established in the local Universe, its prevalence and drivers at intermediate redshifts remain poorly constrained in representative cluster samples. We investigated the incidence, accretion state, and host-galaxy properties of AGNs in BCGs residing in Sunyaev--Zel'dovich-selected clusters in the redshift range 0.3 < z < 0.8, testing dependences on cosmic epoch, cluster mass, and cluster dynamical state. We analysed 171 BCGs drawn from the Atacama Cosmology Telescope Sunyaev--Zel'dovich catalogue, combining Southern African Large Telescope spectroscopy, WISE mid-infrared photometry, and Rapid ASKAP Continuum Survey radio data with spectral energy distribution modelling to derive stellar masses, star formation rates, and Eddington-scaled accretion rates. X-CIGALE Thirty-eight BCGs (22%) host radio-loud AGNs. Only two (∼5%) are classified as high-excitation radio galaxies; the remainder are low-excitation systems. Most AGNs occupy low Eddington ratios (-3 łesssim λ_ 10 Edd łesssim -1), consistent with predominantly radiatively inefficient accretion. Accretion efficiency increases with redshift, whereas only weak or statistically insignificant correlations are found with cluster mass and dynamical state. Radio luminosity is independent of cluster mass. Compared to field radio AGNs, BCG radio-loud AGNs exhibit similar radio powers but are hosted by galaxies that are, on average, sim0.8 dex more massive. BCG radio-loud AGNs at 0.3 < z < 0.8 are predominantly low-excitation, radiatively inefficient systems, indicating that maintenance-mode accretion was already widespread in massive clusters (M_ 500c ≃ 3.2 ,M_⊙) by z ∼ 1. The observed trends suggest that black hole accretion is regulated primarily by fuel availability and cosmic evolution rather than by global cluster properties, while the cluster environment mainly influences the characteristic host-galaxy mass scale. 10^ 14