A minimalist merger interpretation of XRISM gas velocity measurements in the Coma cluster

The recent microcalorimetric X-ray observations of the Coma cluster by XRISM have prompted 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 ≃100 − 200 km s −1 in the cluster core. This merger scenario was originally proposed 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.