From outskirts to core: the suppression and activation of radio AGN around galaxy clusters

TL;DR

This study maps the distribution of radio AGN around galaxy clusters, revealing complex radial trends in AGN fraction and luminosity that suggest environmental influences on AGN activity.

Contribution

It provides the first detailed analysis of radio AGN distribution out to 30 times the cluster radius, uncovering radial variations in AGN fraction and host galaxy properties.

Findings

AGN fraction peaks in cluster outskirts and core, dips at intermediate radii.

Higher AGN fractions correlate with more radio luminous AGN.

Inner regions host more massive galaxies with AGN.

Abstract

To investigate how the radio-identified active galactic nuclei (AGN) fraction varies with cluster-centric radius, we present the projected and de-projected distributions of a large sample of LOFAR-identified radio AGN out to $30R_{500}$ around galaxy clusters. The AGN fraction experiences a $\sim 25\%$ increase above the field fraction in the cluster outskirts at around $10R_{500}$, a $\sim 20\%$ decrease around $\sim 0.5R_{500}$, and an increase of over three times the field fraction value in the very cluster core. We label these three radial windows the outer, intermediate and inner regions respectively, and investigate how these radial trends might arise due to intrinsic properties of the AGN population. The only difference seen in host galaxy stellar mass is in the inner region, where there is a much higher fraction of massive host galaxies. Analysing AGN radio luminosity, regions with a higher AGN fraction tend to have more radio luminous AGN, and vice versa. We discuss the physical mechanisms that might be responsible for these results with reference to the literature.