The bulk motion of gas in the core of the Centaurus galaxy cluster

TL;DR

This study uses XRISM X-ray spectroscopy to measure bulk gas motions in the Centaurus cluster core, revealing velocities consistent with sloshing and limited AGN influence, which impacts heat distribution and cooling processes.

Contribution

First direct measurement of gas bulk motions in the Centaurus cluster core using XRISM, providing insights into ICM dynamics and AGN feedback effects.

Findings

Gas flows along the line of sight with velocities 130-310 km/s.

Bulk motions are consistent with core gas sloshing.

Gas velocity dispersion is less than 120 km/s, indicating limited AGN influence.

Abstract

Galaxy clusters, the largest gravitationally bound structures in the Universe, contain vast amounts of dark matter, galaxies, and hot ionised gas known as the intracluster medium (ICM). In relaxed cluster cores, the ICM appears to cool radiatively faster than the age of the cluster, but the Galaxy clusters contain vast amounts of hot ionised gas known as the intracluster medium (ICM). In relaxed cluster cores, the radiative cooling time of the ICM is shorter than the age of the cluster, but the absence of line emission associated with cooling suggests heating mechanisms that offset the cooling, with feedback from active galactic nuclei (AGNs) being the most likely source. Turbulence and bulk motions, such as the oscillating ("sloshing") motion of the core gas in the cluster potential well, have also been proposed as mechanisms for heat distribution from the outside of the core. Here we present X-ray spectroscopic observations of the Centaurus galaxy cluster with the XRISM satellite. We find that the hot gas flows along the line of sight relative to the central galaxy, with velocities from 130 km/s to 310 km/s within ~30 kpc of the centre. This indicates bulk flow consistent with core gas sloshing. While the bulk flow may prevent excessive accumulation of cooled gas at the centre, it could distribute the heat injected by the AGN and bring in thermal energy from the surrounding ICM. The velocity dispersion of the gas is found to be only ~<120 km/s in the core, even within ~10 kpc of the AGN. This suggests that the AGN's influence on the surrounding ICM motion is limited in the cluster.