Simulating the transport of relativistic electrons and magnetic fields injected by radio galaxies in the intracluster medium

TL;DR

This paper uses simulations to study how relativistic electrons from radio galaxies evolve and spread in galaxy clusters, highlighting the roles of shocks and turbulence in re-accelerating these particles over hundreds of millions of years.

Contribution

The study introduces a novel simulation approach with passive tracer particles to model electron spectrum evolution, including energy losses and re-acceleration in the intracluster medium.

Findings

Relativistic electrons from radio galaxies can fill the intracluster medium over hundreds of millions of years.

Fossil electrons created by radio galaxies serve as a reservoir for re-acceleration by shocks and turbulence.

The evolution of radio lobes is significantly influenced by intracluster medium dynamics.

Abstract

Radio galaxies play an important role in the seeding of cosmic rays and magnetic fields in galaxy clusters. Here, we simulate the evolution of relativistic electrons injected into the intracluster medium by radio galaxies. Using passive tracer particles added to magnetohydrodynamical adaptive-mesh simulations, we calculate the evolution of the spectrum of relativistic electrons taking into account energy losses and re-acceleration mechanisms associated with the dynamics of the intracluster medium. Re-acceleration can occur at shocks via diffusive shock acceleration, and in turbulent flows via second-order Fermi re-acceleration. This study confirms that relativistic electrons from radio galaxies can efficiently fill the intracluster medium over scales of several $100 \rm ~Myr$, and that they create a stable reservoir of fossil electrons that remains available for further re-acceleration by shock waves and turbulent gas motions. Our results also show that late evolution of radio lobes and remnant radio galaxies is significantly affected by the dynamics of the surrounding intracluster medium. Here the diffusive re-acceleration couples the evolution of relativistic particles to the gas perturbations. In the near future, deep radio observations, especially at low frequencies, can probe such mechanisms in galaxy clusters.