Simulations of two-temperature jets in galaxy clusters: I. Effect of jet magnetization on dynamics and electron heating

TL;DR

This study uses 3D magnetohydrodynamic simulations to explore how jet magnetization affects electron and proton heating in galaxy cluster jets, revealing protons dominate energy while electrons approach equipartition through turbulence.

Contribution

It introduces a variable electron heating model in two-temperature MHD simulations, highlighting the impact of jet magnetization on energy distribution and radio cavity characteristics.

Findings

Protons gain most of the jet's kinetic energy via shocks and turbulence.

Electrons tend toward energy equipartition with magnetic energy.

The model explains radiatively inefficient cavities but not efficient ones, suggesting pair-plasma presence.

Abstract

Non-radiating protons in the radio lobes have an essential role to form the jet morphology which is shown by recent radio and X-ray observations. However, since protons and electrons are not always in energy equilibrium due to weak Coulomb coupling, it is difficult to estimate the energy contribution of protons for inflation of radio lobes. The main focus of this study is to examine the effect of the variable model for electron heating by turbulence and shock waves on the thermal energy distribution of electron and proton. We performed two-temperature three-dimensional magnetohydrodynamic simulations of sub-relativistic jets in the galaxy cluster while varying jet magnetization parameters. Because the energy partition rate between electrons and protons in shock and turbulence is determined by plasma kinetic scale physics, our global simulations include electron instantaneous heating sub-grid models for shock waves and turbulence. We find that most of the bulk kinetic energy of the jet is converted into thermal energy of protons through both shocks and turbulence. Thus, protons are energetically dominant. Meanwhile, thermal electrons stored in the lobe evolve toward energy equipartition with magnetic energy through turbulent dissipation. We further estimated the radio power and the mechanical jet power of radio lobes following the same method as used for radio and X-ray observations, and compared these powers with that of the observed radio jets. The two-temperature model quantitatively explains the radiatively inefficient radio cavities, but cannot reproduce the radiatively efficient cavity, even for strong magnetized jets. This implies that a significant population of pair-plasma is needed in the radiatively efficient radio cavities.