Disentangling Multiple Gas Kinematic Drivers in the Perseus Galaxy Cluster

Abstract

Galaxy clusters, the Universe's largest halo structures, are filled with 10-100 million degree X-ray-emitting gas. Their evolution is shaped by energetic processes such as feedback from supermassive black holes (SMBHs) and mergers with other cosmic structures. The imprints of these processes on gas kinematic properties remain largely unknown, restricting our understanding of gas thermodynamics and energy conversion within clusters. High-resolution spectral mapping across a broad spatial-scale range provides a promising solution to this challenge, enabled by the recent launch of the XRISM X-ray Observatory. Here, we present the kinematic measurements of the X-ray-brightest Perseus cluster with XRISM, radially covering the extent of its cool core. We find direct evidence for the presence of at least two dominant drivers of gas motions operating on distinct physical scales: a small-scale driver in the inner ~60 kpc, likely associated with the SMBH feedback; and a large-scale driver in the outer core, powered by mergers. The inner driver sustains a heating rate at least an order of magnitude higher than the outer one. This finding suggests that, during the active phase, the SMBH feedback generates turbulence, which, if fully dissipated into heat, could play a significant role in offsetting radiative cooling losses in the Perseus core. Our study underscores the necessity of kinematic mapping observations of extended sources for robust conclusions on the properties of the velocity field and their role in the assembly and evolution of massive halos. It further offers a kinematic diagnostic for theoretical models of SMBH feedback.

Figures (13)

• Figure 1: High-resolution X-ray image and spectrum of the Perseus cluster. (a) X-ray surface brightness divided by the best-fit model of the mean surface brightness profile, centered at RA=49.9508 and Dec=41.5115 (J2000). The $2-8$ keV image is obtained from Chandra observations with a total cleaned exposure time $\simeq 1.4$ Ms and smoothed with a 1" Gaussian. The redshift is taken to be $z=0.017284$ (redshift of the BCG), so that 1' corresponds to a physical scale of $22{\rm \,kpc}$ (for a standard cosmology with $h=0.67$, $\Omega_{\rm m}=0.32$, $\Omega_{\Lambda}=0.68)$. White squares indicate XRISM/Resolve pixels for the four pointings centered at distances of $\sim 0,\ 68,\ 133$, and $200$ kpc from the center, with pixels 12 and 27 removed. (b) XRISM/Resolve spectrum in units of $\rm counts{\rm \,s}^{-1}{\rm \,keV}^{-1}$, extracted from the entire central pointing in the $3-11{\rm \,keV}$ energy range, highlighting several prominent emission lines. The spectrum is based on the combined data from ObsIDs 000154000 and 000155000, resulting in a total exposure time of 98 ks. The inset provides a closer look at the strongest Fe XXV He-$\alpha$ line complex. The observed spectrum is shown in black, with the best-fit spectral model overlaid in red (Methods).
• Figure 1: X-ray structures within the Perseus core and default radial binning scheme adopted for the analysis. (a) Residual X-ray/Chandra image of the Perseus cluster in the $2-8{\rm \,keV}$ band, with arrows highlighting prominent structures relevant to our analysis. (b) The color pixels and grey circles/annuli show detector and sky regions (No. 1–6 from inner to outer), respectively, with the black dashed circle marking the innermost sky region. White contours illustrate the regions that contribute 90% photons to each pointing based on our SIXTE simulations.
• Figure 2: Radial profile of gas kinematic properties in the Perseus cluster measured with XRISM/Resolve. (a) LOS velocity dispersion $\sigma_{\rm ICM}$ measured from the broadening of emission lines present in the 3--11 keV energy range (red). In the innermost two regions, the width of the strongest Fe XXV He-$\alpha$ is decoupled from the broadening of other lines since its shape is affected by resonant scattering (Methods). Yellow shaded region indicates predictions from numerical simulations of stratified turbulence driven on $500$ kpc scale in the Perseus-like atmosphere (Methods), with the scatter corresponding to the standard deviation of the velocity dispersion. (b) LOS bulk velocity of the gas obtained from centroid shifts of all emission lines in the 3--11 keV energy range relative to the heliocentrically-corrected bulk velocity of the central galaxy NGC 1275. Vertical error bars show $1\sigma$ statistical uncertainty. Systematic uncertainties, discussed in Methods, could result in velocity variations within the $1 \sigma$ range. Calibration uncertainties of the velocity dispersion and bulk velocity are $<10{\rm \,km\,s^{-1}}$ and $\simeq18{\rm \,km\,s^{-1}}$ (Methods), respectively. The gray curve represents the profile of residual X-ray surface brightness in the band $0.5-8{\rm \,keV}$ extracted from the region covered by the XRISM pointings.
• Figure 2: Constraints on AGN parameters: photon index $\Gamma$ vs. flux between $2-10{\rm \,keV}$. The contours indicate the implied 1, 2, $3\sigma$ parameter regimes from the two independent approaches utilizing Chandra spectra for the ICM component. Pink contours are based on the ratio of fluxes between sky regions 1/2 and 1/3 in the $4-6{\rm \,keV}$ band, which lacks strong emission lines, while blue contours are from the measurements of the equivalent width of Fe He-$\alpha$ line complex (Methods). For modeling the ICM in this work, we fixed the AGN flux at $31\times 10^{-12}{\rm \,erg}{\rm \,s}^{-1}{\rm \,cm}^{-2}$, shown as the black point with $1\sigma$ error bars of the photon index.
• Figure 3: Kinematic maps of the hot gas in the Perseus cluster. Velocity dispersion (a) and bulk velocity (b) maps are overlaid on the X-ray residual image (grey). The maps show azimuthal variations in the inner $\simeq30$ kpc region and radial variations in narrow bins outside this region. Statistical uncertainties for each region are shown in Extended Data Fig. \ref{['fig:map_bins_error']}.