A Minimalist Merger Interpretation of XRISM's Gas Velocity Measurements in the Coma Cluster

TL;DR

This paper proposes that an early off-axis minor merger can explain XRISM's gas velocity observations in the Coma cluster, highlighting a simple diagnostic for intracluster gas motions.

Contribution

It introduces a minimalist merger model to interpret gas velocities and a new diagnostic based on velocity ratios, advancing understanding of cluster dynamics.

Findings

Merger scenario reproduces observed velocity features.

Velocity dispersion remains approximately uniform at 100-200 km/s.

Diagnostic based on velocity to dispersion ratio effectively characterizes gas motions.

Abstract

The recent microcalorimetric X-ray observations of the Coma cluster by XRISM have sparked active discussion regarding the physical origin of its gas velocity features. Here, we demonstrate that an off-axis minor merger in its early phase $-$ when the infalling subhalo is near its primary apocenter and the stripped tail is not yet mixed with the main cluster atmosphere $-$ can drive intracluster gas motions generally consistent with the XRISM results. These include a pronounced velocity gradient and an approximately uniform velocity dispersion of $\simeq100-200\,\rm{km\,s^{-1}}$ in the cluster core. Our merger scenario was originally suggested in Lyskova et al. (2019) to reproduce the major X-ray morphological features of Coma. In addition, we introduce a simple and robust diagnostic of intracluster gas motions based on the ratio of the line-of-sight velocity to the velocity dispersion.