Establish whether charge exchange contributes to Perseus line ratios

Establish whether charge exchange contributes materially to the measured iron emission-line ratios in the central regions of the Perseus intracluster medium and quantify its spatial variation.

Background

The analysis does not include charge exchange, despite the presence of cold H-alpha filaments in the central Perseus region where the process could occur. Previous observations provide hints of charge-exchange contamination, and preliminary modeling suggests a comparable level for the iron He-alpha lines.

Because the contamination may vary between regions, determining its presence and amplitude is relevant to interpreting the resonant-scattering line ratios and the inferred gas velocities.

References

Charge exchange has yet to be conclusively detected in the ICM; however, it is likely to occur in the central regions of Perseus where cold H$\alpha$ filaments reside \citep[e.g.][]{gendron-marsolais2018}.

— 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 4.3, “Systematic uncertainties,” subsection “Charge exchange”