Life cycle of cosmic-ray electrons in the intracluster medium

TL;DR

This study models how cosmic-ray electrons injected by a central radio galaxy evolve within a galaxy cluster, highlighting the importance of re-acceleration processes in maintaining long-lived radio emissions and explaining observed cluster-wide radio phenomena.

Contribution

It introduces a coupled simulation approach to study the dispersal and energy evolution of cosmic-ray electrons influenced by jet power and re-acceleration in galaxy clusters.

Findings

Re-acceleration is crucial for long-lived fossil electron reservoirs.

Absence of major mergers limits detectable radio emissions.

Jet power influences electron dispersal and cluster emission properties.

Abstract

We simulate the evolution of relativistic electrons injected into the medium of a small galaxy cluster by a central radio galaxy, studying how the initial jet power affects the dispersal and the emission properties of radio plasma. By coupling passive tracer particles to adaptive-mesh cosmological MHD simulations, we study how cosmic-ray electrons are dispersed as a function of the input jet power. We also investigate how the latter affects the thermal and non-thermal properties of the intracluster medium, with differences discernible up to $\sim$ Gyr after the start of the jet. We evolved the energy spectra of cosmic-ray electrons, subject to energy losses that are dominated by synchrotron and inverse Compton emission as well as energy gains via re-acceleration by shock waves and turbulence. We find that in the absence of major mergers the amount of re-acceleration experienced by cosmic-ray electrons is not enough to produce long-lived detectable radio emissions. However, for all simulations the role of re-acceleration processes is crucial to maintain a significant and volume-filling reservoir of fossil electrons ($\gamma \sim 10^3$) for several Gyrs after the first injection by jets. This is important to possibly explain recent discoveries of cluster-wide emission and other radio phenomena in galaxy clusters.