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

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 $124\pm 21~{\rm km\, s^{-1}}$, corresponding to a subsonic Mach number of $0.19\pm 0.03$, while a finite line-of-sight bulk velocity of $263\pm 23~{\rm km\, s^{-1}}$ 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, suggesting 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.