Bulk and turbulent gas motions in the interacting galaxy cluster Abell 3395 South observed with XRISM

TL;DR

This study uses XRISM high-resolution X-ray spectroscopy to measure gas motions in the galaxy cluster Abell 3395 South, revealing low turbulence but significant bulk flow, indicating a non-relaxed dynamical state.

Contribution

First direct measurement of both bulk and turbulent velocities in A3395S using XRISM, demonstrating the capability of high-resolution X-ray spectroscopy to study cluster dynamics.

Findings

Low turbulent velocity of 124±21 km/s

Significant line-of-sight bulk velocity of 263±23 km/s

Cluster not yet dynamically relaxed

Abstract

We investigate the gas motions in the core region of the Abell~3395 South subcluster (A3395S) using high-resolution X-ray spectroscopy with XRISM/Resolve. By analyzing the Fe~XXV He$\alpha$ emission line, we directly measure the line-of-sight bulk and turbulent velocities of the intracluster medium. We find that the one-dimensional turbulent velocity is low, at the level of $124\pm21~{\rm km\,s^{-1}}$, while a significant line-of-sight bulk velocity of $263\pm23~{\rm km\,s^{-1}}$ is detected. The coexistence of low turbulence and finite bulk motion suggests that A3395S has not yet reached a dynamically relaxed state. These results are consistent with the non-detection of a radio halo in A3395S, implying that turbulent particle reacceleration is currently inefficient in the cluster core. This study demonstrates that high-resolution X-ray spectroscopy with XRISM provides a powerful means to directly constrain intracluster medium dynamics in merging galaxy clusters, and it provides a reference for future comparative studies of A3395N and A3391 within the same large-scale structure.