Resolve the anisotropy of central intracluster-medium motions

Determine whether the small-scale gas motions in the central approximately 10–20 kpc of the Perseus cluster are isotropic, purely radial, or purely tangential by obtaining observations with sufficient spatial resolution and statistical precision to distinguish the predicted resonant-scattering signatures.

Background

The authors simulate isotropic, radial, and tangential velocity fields. The present data are consistent with isotropic or radial motions, while purely tangential motions are somewhat disfavored but not excluded because Doppler broadening and resonant scattering may probe different spatial scales.

The paper identifies improved statistics and spatial binning of the central approximately 10 kpc as the means to resolve the competing anisotropy scenarios.

References

Therefore, our analysis slightly disfavors a scenario wherein gas motions in the inner $\sim 20$ kpc region of Perseus are purely tangential. However, we cannot rule out this scenario given the nontrivial difference in scales probed by Doppler broadening and resonant scattering.

— XRISM observations of the Perseus cluster along two arms: Chaotic ICM motions probed by resonant scattering  (2609.10845 - Heinrich et al., 9 Sep 2026) in Section 4.2, “Resonant scattering simulations: anisotropic gas motions”; also Section 5, “Conclusions”