Disentangling AGN Feedback and Sloshing in the Perseus Cluster with XRISM: Insights from Simulations

TL;DR

This work tackles the origin of the complex velocity field in the Perseus cluster as revealed by XRISM by performing controlled AREPO MHD simulations that isolate and combine merger-driven sloshing with AGN jet feedback. The authors generate synthetic X-ray observables, including emissivity, line-of-sight velocity dispersions, and Fe XXV line profiles, to compare with XRISM data. They find that neither mechanism alone can reproduce the observed non-monotonic dispersion; only the combination of sloshing and AGN feedback matches the central and outer dispersions, with sloshing shaping large-scale motions and jets driving core turbulence. Velocity-power spectra reveal distinct signatures: sloshing yields large-scale coherence with a steep spectrum, while AGN-driven turbulence injects small-scale power in the core, producing broader, multi-component lines in the center. The results highlight the necessity of multi-scale, multi-driver modeling to interpret high-resolution X-ray spectroscopy and provide concrete observational diagnostics for future XRISM analyses and related simulations.

Abstract

High-resolution X-ray spectroscopy with XRISM has revealed complex, non-monotonic velocity dispersion profiles in the Perseus cluster, pointing to a complex interplay between at least two physical drivers of motions caused by dynamical processes within the intracluster medium (ICM). To further explore this conclusion, we perform a suite of idealized, controlled simulations targeting the relative roles of merger-induced sloshing and active galactic nucleus (AGN) feedback. Our models systematically isolate and combine these mechanisms to predict observable velocity profiles and X-ray line shapes, providing direct comparison to XRISM and Hitomi data. We find that neither sloshing nor AGN activity alone can reproduce the observed velocity dispersion profile; only their combined action matches the elevated dispersions both at the cluster core and outskirts. Power-spectrum analysis reveals distinct spatial signatures: sloshing generates large-scale coherent motions, while AGN feedback injects turbulence and broadens the velocity spectrum at small scales, especially in the core. By forward-modeling spectral line profiles, we show how these dynamics imprint unique observational signatures on X-ray emission. Our results underscore the necessity of accounting for both large-scale and small-scale drivers of gas motions in the ICM when interpreting high-resolution spectroscopic data, and provide guidance for the analysis of forthcoming XRISM observations.

Figures (8)

• Figure 1: The black crosses correspond to the velocity dispersion values and their error bars observed by XRISM xrism_perseus_2025. The blue shaded area illustrates results from a sloshing-only simulation, the orange region shows an AGN-only simulation, and the green and light green regions correspond to simulations with AGN jet feedback with different powers included in the same sloshing system. The solid lines correspond to the mean azimuthal values of the emission-weighted velocity dispersion, and the shaded regions indicate the standard deviation from the mean. All simulations were initialized identically and are shown at the same epoch, $\sim 1.1$ Gyr after pericenter passage. AGN jet feedback is introduced approximately 1 Gyr after the subcluster pericenter passage and persists for 100 Myr. The merger plane is taken to be the plane of the sky.
• Figure 2: Velocity dispersion profiles from simulations exploring different merger configurations compared to the observed values in Perseus xrism_perseus_2025. The blue shaded region shows results from our fiducial sloshing-only simulation (mass ratio $R = 1:5$, incident angle $\theta = 20^\circ$, which leads to an impact parameter $\sim 1026$ kpc). The orange shaded region illustrates the effect of a more massive subcluster infalling onto the main cluster ($R = 1:2$), which increases the overall velocity dispersion at all radii but still fails to increase the velocity dispersion in the cluster core. The red shaded region corresponds to a simulation with a reduced impact parameter ($\sim 520$ kpc, achieved by setting the incident angle $\theta = 10^\circ$ while keeping the mass ratio fixed). The solid lines and shades correspond to the mean values and standard deviation of the emission-weighted velocity dispersion, respectively.
• Figure 3: Velocity power spectra in four distinct 100-kpc-wide cubic regions for two simulations. Left panels: locations of the cubes overlaid on X-ray surface brightness Gaussian Gradient Magnitude-filtered maps for the sloshing-only simulation (top) and the simulation including both sloshing and AGN feedback with jets of power $10^{45}$ erg s$^{-1}$ (AGN+sloshing, bottom). The cubes are labeled in the right panels by location, including the cluster center (blue), a region exhibiting KHI structures (orange), a cold front surface (CF, green), and a region out of the plane (red). Right panels: corresponding velocity power spectra for each cube, with colors matching the cube locations. In the sloshing-only case, all regions exhibit similar power spectra dominated by large-scale motions and steep slopes, indicating limited small-scale structure. In contrast, the central region in the AGN simulation shows enhanced power and a flatter slope, consistent with the injection of kinetic energy on smaller scales by AGN-driven activity.
• Figure 4: Slices of the $x$, $y$, $z$ components of the velocity field through the cluster core for the simulation including both sloshing and AGN jets with power $1 \times 10^{45}$ erg s$^{-1}$, launched along the $y$-axis.
• Figure 5: Velocity structure of three pointings. The background shows a map of the projected bulk velocity field along the line of sight, with three $60\times60$ kpc$^2$ XRISM-like pointings overlaid. The green pointing is centered on the potential minimum, representing the core, while the blue and purple pointings are positioned along the diagonal arm, following the observational approach of xrism_perseus_2025. The inset panels display two-dimensional histograms of the X-ray emissivity-weighted line-of-sight velocity ($v_z$) as a function of projected distance along the sightline ($z$), in the $6–8$ keV band, extracted from prisms 1 Mpc deep. The magenta line is the weighted average profile of the LOS velocity along the line of sight. Panel frames correspond to each pointing's color; the top row presents the velocity structure for the sloshing-only case, while the bottom row shows the combined sloshing and AGN jet scenario.