The Lack of Non-Thermal Motions in Galaxy Cluster Cores

TL;DR

This study finds that non-thermal motions in galaxy cluster cores are minimal, supporting the validity of hydrostatic equilibrium assumptions for mass estimates in these regions.

Contribution

First detailed 3D analysis combining lensing, X-ray, and SZE data showing minimal non-thermal pressure in cluster cores.

Findings

Non-thermal pressure fraction is consistent with zero within 0.1R200m.

Non-thermal pressure increases to about 20% at 0.4R200m.

Little variation in non-thermal pressure across different cluster dynamical states.

Abstract

We report the non-thermal pressure fraction (Pnt/Ptot) obtained from a three-dimensional triaxial analysis of 16 galaxy clusters in the CLASH sample using gravitational lensing (GL) data primarily from Subaru and HST, X-ray spectroscopic imaging from Chandra, and Sunyaev-Zel'dovich effect (SZE) data from Planck and Bolocam. Our results span the approximate radial range 0.015-0.4R200m (35-1000 kpc). At cluster-centric radii smaller than 0.1R200m the ensemble average Pnt/Ptot is consistent with zero with an upper limit of nine per cent, indicating that heating from active galactic nuclei and other relevant processes does not produce significant deviations from hydrostatic equilibrium (HSE). The ensemble average Pnt/Ptot increases outside of this radius to approximately 20 per cent at 0.4R200m, as expected from simulations, due to newly accreted material thermalizing via a series of shocks. Also in agreement with simulations, we find significant cluster-to-cluster variation in Pnt/Ptot and little difference in the ensemble average Pnt/Ptot based on dynamical state. We conclude that on average, even for diverse samples, HSE-derived masses in the very central regions of galaxy clusters require only modest corrections due to non-thermal motions.