A XRISM/Resolve view of the dynamics in the hot gaseous atmosphere of M87

TL;DR

This study uses XRISM/Resolve to measure gas velocities in M87's core, revealing high turbulence and shock-driven motions that inform understanding of AGN feedback in galaxy clusters.

Contribution

First direct measurement of gas velocities in M87's core with XRISM, providing detailed insights into turbulence and shock dynamics at small scales.

Findings

High velocity dispersion near the AGN (~262 km/s)

Decline in turbulence with radius, reaching ~60 km/s

M87's core shows the highest turbulence among observed clusters

Abstract

The XRISM/Resolve microcalorimeter directly measured the gas velocities in the core of the Virgo Cluster, the closest example of AGN feedback in a cluster. This proximity allows us to resolve the kinematic impact of feedback on scales down to 5 kpc. Our spectral analysis reveals a high velocity dispersion of $\sigma_v$=262 (+45 / -38) km/s near the AGN, which steeply declines to ~60 km/s between 5 and 25 kpc in the northwest direction. The observed line-of-sight bulk velocity in all regions is broadly consistent with the central galaxy, M87, with a mild trend toward blueshifted motions at larger radii. Systematic uncertainties have been carefully assessed and do not affect the measurements. The central velocities, if attributed entirely to isotropic turbulence, correspond to a transonic ICM at sub-6 kpc scales with three-dimensional Mach number 0.69 (+0.14 / -0.11) and a non-thermal pressure fraction of 21 (+7 / -5)%. Simple models of weak shocks and sound waves and calculations assuming isotropic turbulence both support the hypothesis that the velocity field reflects a mix of shock-driven expansion and turbulence. Compared to other clusters observed by XRISM to date, M87's central region stands out as the most kinematically disturbed, exhibiting both the highest velocity dispersion and the largest 3D Mach number, concentrated at the smallest physical scales.