XMM-Newton view of X-ray overdensities from nearby galaxy clusters: The environmental dependencies

Abstract

In this work, we studied ten nearby (z≤0.038) galaxy clusters in order to understand possible interactions between hot plasma and member galaxies within cluster's po- tential well. A multi-band source detection technique was applied to detect point-like structures within the intra-cluster medium (ICM). We studied spectral properties of a total of 391 X-ray point sources within the cluster field. Log N - Log S was studied in the energy range of 2-10 keV to measure X-ray overdensities. Optical overdensities were calculated for our sample of clusters, and we compared X-ray and optical over- densities to solve suppression/triggering phenomena for nearby galaxy clusters. Both X-ray to optical flux/luminosity properties, (X/O, LX/LB, LX/LK), were investigated for optically identified member galaxies. We found that X-ray luminosity values of our point sources are faint (40.08 ≤ log(LX) ≤ 42.39 erg s-1). The luminosity range of point sources reveals possible contributions to X-ray emission from low luminos- ity active galactic nuclei (LLAGNs), X-ray Binaries (XRBs) and star formation. We calculated ~ 2 times higher X-ray overdensities from galaxies within galaxy clusters compared to fields. Our results demonstrate that optical overdensities are much higher than X-ray overdensities at the cluster's centre, whereas X-ray overdensities increase through the outskirts of clusters. We conclude that high pressure from the cluster's centre affects the balance of galaxies, hereby they lose a significant amount of their fuels; as a result, clustering process quenches X-ray emission of the member galax- ies. On the other hand, we found evidence that the existence of X-ray bright sources within cluster environment can be explained by two main phenomena: contributions from off-nuclear sources and/or AGN triggering caused by galaxy interactions rather than AGN fuelling.