Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Eugene Churazov, Ildar Khabibullin, Natalya Lyskova, Rashid Sunyaev, Klaus Dolag

TL;DR

The Perseus cluster is mapped from its cool core to its virial outskirts by merging SRG/eROSITA X-ray data with archival XMM-Newton and Chandra observations, yielding a uniform, high-resolution view up to $R_{200c}$. The analysis identifies IC310 as the center of a merging subcluster and reveals a dramatic, loop-like radio tail in IC310, alongside a high-velocity tail in NGC1265, indicative of a merger-driven ICM flow and near-apocenter dynamics. A beta-model residual analysis highlights East–West merger perturbations, while dynamical arguments, 2MASS filament context, and Magneticum simulations quantify the merger timing (a few Gyr) and the rarity of the observed LOS velocities, with a plausible geometry along the Perseus-Pisces filament. The findings demonstrate how wide-field X-ray surveys, when combined with multi-wavelength data, illuminate the assembly history of nearby massive clusters and constrain merger-driven ICM dynamics that shape radio tails and gas sloshing.

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.

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

TL;DR

The Perseus cluster is mapped from its cool core to its virial outskirts by merging SRG/eROSITA X-ray data with archival XMM-Newton and Chandra observations, yielding a uniform, high-resolution view up to . The analysis identifies IC310 as the center of a merging subcluster and reveals a dramatic, loop-like radio tail in IC310, alongside a high-velocity tail in NGC1265, indicative of a merger-driven ICM flow and near-apocenter dynamics. A beta-model residual analysis highlights East–West merger perturbations, while dynamical arguments, 2MASS filament context, and Magneticum simulations quantify the merger timing (a few Gyr) and the rarity of the observed LOS velocities, with a plausible geometry along the Perseus-Pisces filament. The findings demonstrate how wide-field X-ray surveys, when combined with multi-wavelength data, illuminate the assembly history of nearby massive clusters and constrain merger-driven ICM dynamics that shape radio tails and gas sloshing.

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 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 . 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.

Paper Structure

This paper contains 19 sections, 2 equations, 15 figures.

Table of Contents

  1. Introduction
  2. X-ray data
  3. Large-scale image
  4. 2MASS
  5. X-ray composite image
  6. Departures from a symmetric model
  7. Discussion
  8. Merger geometry and timing
  9. Substructure near the virial radius
  10. Two prominent radio galaxies
  11. IC310
  12. NGC1265
  13. Test particle (NGC1265) in a static potential
  14. Line-of-sight velocities in simulations
  15. Conclusions
  16. ...and 4 more sections

Figures (15)

  • Figure 1: 10x10 degrees patch of the sky centered at the Perseus cluster in equatorial coordinates. The estimated turnaround radius of the Perseus cluster is $\sim 7^\circ$, i.e., the entire image falls within the turnaround radius. Left: eROSITA 0.4-2.3 keV X-ray image; middle: $y$-map from PLANCK based on PR4 maps 2023MNRAS.526.5682C; right: dust extinction map 2019ApJ...887...93G. Two X-ray and SZ-bright objects on the right are the galaxy clusters AWM7/2A0251+413 ($z\sim 0.0172$) and CIZAJ0300.7+4427 ($z\sim 0.030$). These two clusters possibly trace the topology of LSS filaments, in particular, AWM7, which belongs to the Perseus-Pisces supercluster 2021AA...651A..16B. CIZAJ0300.7+4427 belongs to another (more distant) filament, which is also seen in the distribution of galaxies (see Sect. \ref{['s:2mass']}). The correspondence between X-ray and Y maps is very good, with the visible SZ signal being less peaked at the center but, as expected, extending to large radii. The "dip" in the very core of the $y$-map is due to contamination by the radio galaxy NGC1275 (Perseus A) and its immediate vicinity. The right figure shows the complexity of the foreground distribution of the Milky Way gas (as traced by dust) in the direction of Perseus. The map is plotted in units of $A_V$ extinction.
  • Figure 2: Positions and recession velocities of 2MASS galaxies in the vicinity of NGC1275 with velocities in the range $\pm 3000\,{\rm km\,s^{-1}}$ relative to NGC1275. The size of the symbols reflects the K magnitudes of a galaxy (brighter - larger), and the color characterizes the line-of-sight velocity relative to NGC1275 in ${\rm km\,s^{-1}}$ (see the color bar on the right side of the plot). Left: 20x20 degrees images showing large-scale filaments. Two of them are marked with black lines. Right: 2x2 degrees version of the same plot. NGC1275, NGC1265, and IC310 are marked with squares. A clear elongation of galaxies with small line-of-sight velocities in the East-West direction suggests that IC310 is part of a "filament" that spans at least a few degrees. In turn, NGC1265 might be related to another "diagonal" (bottom-left to top-right) filament that has several galaxies with larger recession velocities (blue/purple circles in the plot).
  • Figure 3: Composite X-ray image of the Perseus cluster ($3\times 3$ degrees, 2" pixels) obtained by co-adding eROSITA all-sky data and pointed observations of Chandra and XMM-Newton. The images of individual telescopes were renormalized to have the same X-ray flux within the central $3'$ circle as in the eROSITA 0.4-2.3 keV band. Radial weights have been applied to ensure that the sharpest Chandra images dominate within a central $3'$. The inset is a zoomed version of the same image showing the central 1% of the image (in terms of the solid angle, i.e., $0.3\times 0.3$ degrees) and the canonical cool-core design with an AGN (NGC1275) and X-ray cavities inflated by the AGN.
  • Figure 4: The same image as in Fig. \ref{['f:cxee']} after division by the best-fitting radial profile shown in Fig. \ref{['f:radial']}, specifically, $\left (I_X/I_{\rm model}-1 \right )$, where the model is the sum of the best-fitting $\beta$-model and a constant sky background). In addition to the rich substructure in the core, this image shows clear signatures of an ongoing merger, including elongation in the East-West direction and sloshing. Two boxes show the positions of two prominent radio galaxies, IC310 (black) and NGC1265 (cyan), respectively. (See also Fig. \ref{['f:divc_200']} for a smoothed version of the image that emphasizes large-scale structures.)
  • Figure 5: Asymmetric structures in a portion of the X-ray image (smoothed version of Fig. \ref{['f:divc']}) in red and the DSS2-R image in light blue. The DSS image has been lightly processed to emphasize diffuse sources (galaxies) relative to numerous compact sources (e.g., stars). The chain of galaxies that begins with NGC1275 extends up to IC310, which appears to be at the peak of extended X-ray emission to the West of the cluster center. Further to the West (outside of the image), there is a cluster AWM7/2A0251+413 at a redshift similar to the Perseus cluster.
  • ...and 10 more figures