Abstract
We present a study of the distribution of X-ray detected active galactic nuclei (AGN) in the five most massive, M500SZ > 1014 M⊙, and distant, z ∼ 1, galaxy clusters in the Planck and South Pole Telescope (SPT) surveys. The spatial and thermodynamic individual properties of each cluster have been defined with unprecedented accuracy at this redshift using deep X-ray observations. This is an essential property of our sample in order to precisely determine the R500Yx radius of the clusters. For our purposes, we computed the X-ray point-like source surface density in 0.5 R500Yx wide annuli up to a clustercentric distance of 4 R500Yx, statistically subtracting the background and accounting for the respective average density of optical galaxies. We found a significant excess of X-ray point sources between 2 and 2.5 R500Yx at the 99.9% confidence level. The results clearly display for the first time strong observational evidence of AGN triggering in the outskirts of high-redshift massive clusters with such a high statistical significance. We argue that the particular conditions at this distance from the cluster centre increase the galaxy merging rate, which is probably the dominant mechanism of AGN triggering in the outskirts of massive clusters.
Highlights
Supermassive black holes (SMBHs) are at the centre of modern astrophysical research today because they are hosted by every massive galaxy in the local Universe, and because the evolution of the SMBH and its host galaxy appears tightly linked (e.g. Gültekin et al 2009; Zubovas & King 2012)
All SMBHs are thought to undergo active phases, the so-called active galactic nucleus (AGN) phases, during which they accrete the surrounding gas, and they emit an immense amount of energy
We studied the AGN activity in massive and distant clusters as a function of clustercentric distance
Summary
Supermassive black holes (SMBHs) are at the centre of modern astrophysical research today because they are hosted by every massive galaxy in the local Universe, and because the evolution of the SMBH and its host galaxy appears tightly linked (e.g. Gültekin et al 2009; Zubovas & King 2012). There is evidence that the cluster mass plays an important role in the efficiency of ram pressure stripping (Ehlert et al 2015; Koulouridis et al 2018), and the fraction of AGN in cluster galaxies was reported to sharply increase with redshift (Martini et al 2013; Bufanda et al 2017). Further studies are needed to investigate the excess and its cause, and to clarify how it is affected by cluster mass and redshift If confirmed, it will add an important piece of information to our knowledge of AGN and their interplay with their local and largescale environment.
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