Perseus cluster in its X-ray entirety with SRG/eROSITA. Merger and Radio-Uroboroses

TL;DR

This study provides a comprehensive X-ray analysis of the Perseus galaxy cluster, revealing merger dynamics, AGN feedback, and peculiar radio galaxy features through combined data from SRG/eROSITA, XMM-Newton, and Chandra.

Contribution

It offers the first complete X-ray coverage of Perseus up to and beyond R200c, highlighting merger history and radio galaxy morphology in a unified analysis.

Findings

Perseus exhibits a cool-core structure with signs of AGN feedback.

IC310 is identified as the main galaxy of a merging subcluster over 4 Gyr.

Radio galaxy NGC1265 shows a rare line-of-sight motion with distinctive radio tails.

Abstract

The Perseus cluster (Abell 426) is a nearby massive galaxy cluster that spans several degrees. We combined SRG/eROSITA, XMM-Newton, and Chandra data to get a complete coverage of this cluster in X-rays up to $R_{\rm 200c}$ and beyond, although at the largest radii, spatial non-uniformities of the X-ray sky background and foreground dominate. While the Perseus central part represents a canonical cool-core structure with clear signs of AGN Feedback, the outskirts, in turn, serve as a convincing example of a merger-perturbed system. X-ray data suggest that IC310 is the main galaxy of a subcluster that merges with Perseus over the past $\sim 4\,{\rm Gyr}$. Overall, this configuration resembles the merger between the Coma cluster and the NGC4839 group. It is statistically more likely to find a merging group near the apocenter of its orbit. Therefore, it is not surprising that IC310 in Perseus has a relatively small velocity relative to the main cluster, similarly to NGC4839 in Coma. Perseus also hosts a high-velocity radio galaxy, NGC1265 (line-of-sight velocity is almost twice the virial velocity of the main cluster), which is known for its spectacular radio tail. Unless this galaxy has been accelerated by a time-variable potential associated with the merger, it has to move almost along the line of sight through the entire cluster, which would be a rare, but not a truly exceptional configuration. Both galaxies, IC310 and NGC1265, have remarkable radio tails with sharp bends that are reminiscent of a "snake biting its tail". We speculate that these curious shapes are natural consequences of their (different) orbits in Perseus. For IC310, the proximity to the apocenter and the reversal of its radial velocity might play a role. For NGC1265, the nearly line-of-sight motion coupled with the gas motions in the merging system might be important.