A Multi-wavelength Survey of AGN in Massive Clusters: AGN Detection and Cluster AGN Fraction

TL;DR

This study uses multi-wavelength techniques to identify AGN in galaxy clusters, finding that the AGN fraction in clusters is comparable to that in the field, with no strong correlation to cluster properties.

Contribution

It demonstrates the effectiveness of combining optical, X-ray, and IR methods to detect AGN across various luminosities and obscuration levels in galaxy clusters.

Findings

Approximately 25 AGN per cluster identified

No significant difference in AGN fraction between cluster and field galaxies

No correlation between cluster properties and AGN fraction

Abstract

We aim to study the effect of environment on the presence and fuelling of Active Galactic Nuclei (AGN) in massive galaxy clusters. We explore the use of different AGN detection techniques with the goal of selecting AGN across a broad range of luminosities, AGN/host galaxy flux ratios, and obscuration levels. From a sample of 12 galaxy clusters at redshifts 0.5 < z < 0.9, we identify AGN candidates using optical variability from multi-epoch HST imaging, X-ray point sources in Chandra images, and mid-IR SED power-law fits through the Spitzer IRAC channels. We find 178 optical variables, 74 X-ray point sources, and 64 IR power law sources, resulting in an average of ~25 AGN per cluster. We find no significant difference between the fraction of AGN among galaxies in clusters and the percentage of similarly-detected AGN in field galaxy studies (~2.5%). This result provides evidence that galaxies are still able to fuel accretion onto their supermassive black holes, even in dense environments. We also investigate correlations between the percentage of AGN and cluster physical properties such as mass, X-ray luminosity, size, morphology class and redshift. We find no significant correlations among cluster properties and the percentage of AGN detected.