Perseus cluster in its X-ray entirety with SRG/eROSITA

Merger and radio-uroboroses

¹ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1 D-85741 Garching, Germany
² Space Research Institute (IKI), Profsoyuznaya 84/32, Moscow 117997, Russia
³ Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians-Universität München, Scheinerstr.1 81679, München, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 26 July 2025
Accepted: 21 January 2026

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_200c and beyond, although at the largest radii, spatial nonuniformities of the X-ray sky background and foreground dominate. While the Perseus central part represents a canonical cool-core structure with clear signs of active galactic nucleus (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 merged with Perseus over the past ∼4 Gyr. Overall, this configuration resembles the merger between the Coma cluster and the NGC 4839 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 small velocity relative to the main cluster, similarly to NGC 4839 in Coma. Perseus also hosts a high-velocity radio galaxy, NGC 1265, whose line-of-sight (LOS) velocity is almost twice the virial velocity of the main cluster. It is known for its spectacular radio tail. Unless NGC 1265 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 NGC 1265, 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 NGC 1265, the nearly LOS motion coupled with the gas motions in the merging system might be important.