Abstract

Observational constraints on the average radial distribution profile of AGN in distant galaxy clusters can provide important clues on the triggering mechanisms of AGN activity in dense environments and are essential for a completeness evaluation of cluster selection techniques in the X-ray and mm wavebands. The aim of this work is a statistical study with XMM-Newtonof the presence and distribution of X-ray AGN in the large-scale structure environments of 22 X-ray luminous galaxy clusters in the redshift range0.9<z≲1.6compiled by the XMM-NewtonDistant Cluster Project (XDCP). To this end, the X-ray point source lists from detections in the soft band (0.35–2.4 keV) and full band (0.3–7.5 keV) were stacked in cluster-centric coordinates and compared to average background number counts extracted from three independent control fields in the same observations. A significant full-band (soft-band) excess of ∼78 (67) X-ray point sources is found in the cluster fields within an angular distance of8′(4 Mpc) at a statistical confidence level of 4.0σ (4.2σ), corresponding to an average number of detected excess AGN per cluster environment of 3.5 ± 0.9 (3.0 ± 0.7). The data point towards a rising radial profile in the cluster region (r<1 Mpc) of predominantly low-luminosity AGN with an average detected excess of about one point source per system, with a tentative preferred occurrence along the main cluster elongation axis. A second statistically significant overdensity of brighter soft-band-detected AGN is found at cluster-centric distances of 4′–6′(2-3 Mpc), corresponding to about three times the average cluster radiusR200of the systems. If confirmed, these results would support the idea of two different physical triggering mechanisms of X-ray AGN activity in dependence of the radially changing large-scale structure environment of the distant clusters. For high-zcluster studies at lower spatial resolution with the upcoming eROSITA all-sky X-ray survey, the results suggest that cluster-associated X-ray AGN may impose a bias in the spectral analysis of high-zsystems, while their detection and flux measurements in the soft band may not be significantly affected.

Highlights

  • Observational studies of the connection of Active Galactic Nuclei (AGN) with the large-scale environment of massive clusters of galaxies and their mutual cosmic evolution can provide important insights into the physical conditions necessary to trigger or suppress AGN activity in galaxies

  • All results are given in stacked units, that is, the sum of all 22 cluster environments is combined into a single radial X-ray source count profile

  • This translates into a fractional source excess in the distant cluster environments of +9.0% in the soft band and +6.9% in the full band

Read more

Summary

Introduction

Observational studies of the connection of Active Galactic Nuclei (AGN) with the large-scale environment of massive clusters of galaxies and their mutual cosmic evolution can provide important insights into the physical conditions necessary to trigger or suppress AGN activity in galaxies. In this respect, AGN activity can be charted in dependence of the changing environments of galaxy clusters as a function of cluster-centric distance: from the dense cores, to the cluster outskirts, and further out to the matter infall regions and the surrounding cosmic web. The only cluster AGN study with a sizable sample of systems at the epoch 1 < z 1.5 was presented in [12] based on infrared selected clusters from the IRAC Shallow Cluster Survey [13], which found a continuing trend of increasing AGN fractions with redshifts in systems with an average halo mass of ∼1014 M

Objectives
Results
Discussion
Conclusion
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call