Simulations of MHD Instabilities in Intracluster Medium Including Anisotropic Thermal Conduction

TL;DR

This study uses 3D MHD simulations to explore how anisotropic thermal conduction and the heat flux buoyancy instability influence the evolution and thermal stability of galaxy cluster cores, highlighting the suppression of conduction and potential effects of AGN activity.

Contribution

The paper introduces detailed 3D MHD simulations that incorporate anisotropic heat conduction and the HBI to analyze cluster core evolution, revealing the impact of magnetic field orientation on thermal stability.

Findings

HBI reorients magnetic fields, suppressing conduction to less than 1/100th of Spitzer value.

Simulated cores show prolonged thermal collapse due to anisotropic conduction effects.

Magnetic field initial conditions influence the final thermodynamical state of cluster cores.

Abstract

We perform a suite of simulations of cooling cores in clusters of galaxies in order to investigate the effect of the recently discovered heat flux buoyancy instability (HBI) on the evolution of cores. Our models follow the 3-dimensional magnetohydrodynamics (MHD) of cooling cluster cores and capture the effects of anisotropic heat conduction along the lines of magnetic field, but do not account for the cosmological setting of clusters or the presence of AGN. Our model clusters can be divided into three groups according to their final thermodynamical state: catastrophically collapsing cores, isothermal cores, and an intermediate group whose final state is determined by the initial configuration of magnetic field. Modeled cores that are reminiscent of real cluster cores show evolution towards thermal collapse on a time scale which is prolonged by a factor of ~2-10 compared with the zero-conduction cases. The principal effect of the HBI is to re-orient field lines to be perpendicular to the temperature gradient. Once the field has been wrapped up onto spherical surfaces surrounding the core, the core is insulated from further conductive heating (with the effective thermal conduction suppressed to less than 1/100th of the Spitzer value) and proceeds to collapse. We speculate that, in real clusters, the central AGN and possibly mergers play the role of "stirrers," periodically disrupting the azimuthal field structure and allowing thermal conduction to sporadically heat the core.