Comparing XRISM cluster velocity dispersions with predictions from cosmological simulations: are feedback models too ejective?

TL;DR

XRISM Resolve provides direct measurements of ICM velocity dispersions in nine clusters, enabling a stringent test of SMBH feedback models in cosmological simulations. By constructing emission-weighted, XRISM-matched quantities from three simulation suites (TNG-Cluster, GADGET-X, SIMBA-GIZMO) and selecting analogs by halo mass and core state, the study finds that cool-core regions systematically exhibit lower dispersions and kinetic pressure than simulated predictions, by about a factor of $1.5$–$1.7$ and $P_{\rm kin}/P_{\rm tot}$ of $2.2\%$ versus $5$–$6.5\%$. Outside cool cores, agreement improves but rare offsets in A2029 (N1/N2) show extreme deviations, implying that current feedback models may overestimate ejective energy transfer or miss non-thermal physics such as cosmic rays. The results motivate refined feedback prescriptions and expanded XRISM observations, particularly of non-cool-core systems, to better constrain ICM dynamics in the gravity-dominated regime and guide future simulations.

Abstract

The dynamics of the intra-cluster medium (ICM), the hot plasma that fills galaxy clusters, are shaped by gravity-driven cluster mergers and feedback from supermassive black holes (SMBH) in the cluster cores. XRISM measurements of ICM velocities in several clusters offer insights into these processes. We compare XRISM measurements for nine galaxy clusters (Virgo, Perseus, Centaurus, Hydra A, PKS\,0745--19, A2029, Coma, A2319, Ophiuchus) with predictions from three state-of-the-art cosmological simulation suites, TNG-Cluster, The Three Hundred Project GADGET-X, and GIZMO-SIMBA, that employ different models of feedback. In cool cores, XRISM reveals systematically lower velocity dispersions than the simulations predict, with all ten measurements below the median simulated values by a factor $1.5-1.7$ on average and all falling within the bottom $10\%$ of the predicted distributions. The observed kinetic-to-total pressure ratio is also lower, with a median value of $2.2\%$, compared to the predicted $5.0-6.5\%$ for the three simulations. Outside the cool cores and in non-cool-core clusters, simulations show better agreement with XRISM measurements, except for the outskirts of the relaxed, cool-core cluster A2029, which exhibits an exceptionally low kinetic pressure support ($<1\%$), with none of the simulated systems in either of the three suites reaching such low levels. The non-cool-core Coma and A2319 exhibit dispersions at the lower end but within the simulated spread. Our comparison suggests that the three numerical models may overestimate the kinetic effects of SMBH feedback in cluster cores. Additional XRISM observations of non-cool-core clusters will clarify if there is a systematic tension in the gravity-dominated regime as well.

Figures (6)

• Figure 1: The number of simulated analogs of the observed clusters contained in the three simulation suites: TNG-Cluster, The 300 GADGET-X and GIZMO-SIMBA, as a function of the halo mass ($M_{\rm 200c}$). The analogs are selected based on the observed halo mass and core properties (see §\ref{['sec:selection']}).
• Figure 2: Comparison between XRISM observations and simulation predictions of the velocity dispersion. Left panel displays the result for the regime where SMBH feedback should be significant or possibly dominant. This includes central pointings in CCs, the Perseus C1 and the Virgo NW offset pointings, which are within their cooling radius ($\lesssim100$ kpc). Right panel shows the result for the regime least affected by SMBH feedback, including central pointings in NCC clusters and the offset pointings outside the cool cores: Perseus M1 and O1, A2029 N1 and N2. The error bars for the XRISM points represent statistical measurement uncertainties. The simulation points show the median for the corresponding simulated sample, while the error bars show the 68% range of values in the sample ($16^{\rm th}-84^{\rm th}$ percentile envelope). The observed velocity dispersions are systematically lower than the simulation medians, in particular for the SMBH feedback dominated regime.
• Figure 3: Comparison between XRISM observations and simulations predictions of the gas temperature. The descriptions are similar to those in Figure \ref{['fig:sigma']}.
• Figure 4: Comparison between XRISM observations and simulations predictions of the kinetic pressure ratio. The descriptions are similar to those in Figure \ref{['fig:sigma']}.
• Figure 5: The extreme low values of kinetic pressure ratios for A2029 offset pointings N1 ( left) and N2 ( right) in comparison with predictions from the three simulations. The results are shown for 352 simulated clusters at z=0 in TNG-Cluster, 324 clusters in the 300 GADGET-X and GIZMO-SIMBA, where the thermal and kinetic measurements are obtained in a self-similar way to account for the mass effect (see text). The x-axis shows a proxy for the cluster dynamical state, with larger values corresponding to more disturbed clusters (see text for the detailed definition). Filled symbols signify systems with halo mass within the A2029 mass range ($M_{\rm 200c}=10^{14.9\pm0.15}M_\odot$). The solid lines show the medians of the XRISM measurements, and the shaded regions indicate the corresponding $1\sigma$ uncertainties.