Recent achievements on KMHD and applications in the ICM

TL;DR

This paper reviews recent progress in kinetic magnetohydrodynamics (KMHD) and demonstrates its application to modeling the intracluster medium, revealing the importance of KMHD in understanding ICM emission statistics.

Contribution

It introduces a fluid approximation for collisionless plasmas, implements it in a MHD code, and applies it to simulate ICM properties, highlighting the role of KMHD in astrophysical plasma analysis.

Findings

Firehose and mirror instabilities can occur in ICM conditions.

Thermal energy converts to magnetic and kinetic energies.

Small-scale structures (~1 kpc) are generated in simulations.

Abstract

Collisionless plasmas are ubiquitous in the Universe. In general full kinetic equations are needed for a correct description of the physics in such environments. Fluid approximations are, at some special cases, valid. In this work we present the basic equations under such an approximation and the implementation of them in a magnetohydrodynamical code. The numerical simulations are applied for intracluster medium physical properties, i.e. low density but high temperature plasma. We show that, under specific conditions firehose and mirror instabilities may be present. The side effects are the conversion of thermal to magnetic/kinetic energies and the generation of small scale structures ($\sim 1$kpc). We study the changes in the statistics of Faraday rotation measurement, and of the synchrotron polarization, when compared to a standard MHD simulation for the ICM. We conclude that KMHD numerical simulations are mandatory in order to fully understand the statistics of the ICM emission.