Jet interaction with galaxy cluster mergers

TL;DR

This study uses 3D magneto-hydrodynamical simulations to explore how AGN jets interact with galaxy cluster mergers, affecting cosmic ray transport, turbulence, and radio emissions, revealing complex morphologies and re-acceleration processes.

Contribution

It introduces detailed simulations of jet-cluster merger interactions, analyzing cosmic ray propagation, turbulence effects, and radio emission implications, which are novel in modeling these combined phenomena.

Findings

CR material permeates cluster centers within 5-6 Gyr

Turbulent acceleration can outpace electron cooling in over 70% volume

Merger shocks are unlikely to produce significant radio relics without additional processes

Abstract

AGN bubbles in cool-core galaxy clusters are believed to facilitate the transport of cosmic ray electrons (CRe) throughout the cluster. Recent radio observations are revealing complex morphologies of cluster diffuse emission, potentially linked to interactions between AGN bursts and the cluster environment. We perform three-dimensional magneto-hydrodynamical simulations of binary cluster mergers and inject a bi-directional jet at the center of the main cluster. Kinetic, thermal, magnetic and CR energy are included in the jet and we use the two-fluid formalism to model the CR component. We explore a wide range of cluster merger and jet parameters. We discuss the formation of various wide-angle-tail (WAT) and X-shaped sources in the early evolution of the jet and merger. During the last phase of the evolution, we find that the CR material efficiently permeates the central region of the cluster reaching radii of $\sim1$-2 Mpc within $\sim5$-6 Gyr, depending on the merger mass ratio. We find that solenoidal turbulence dominates during the binary merger and explore the possibility for the CR jet material to be re-accelerated by super-Alfv\`enic turbulence and contribute to cluster scale radio emission. We find high volume fractions, $\gtrsim 70$\%, at which the turbulent acceleration time is shorter than the electron cooling time. Finally, we study the merger shock interaction with the CRe material and show that it is unlikely that this material significantly contributes to the radio relic emission associated with the shocks. We suggest that multiple jet outbursts and/or off-center radio galaxies would increase the likelihood of detecting these merger shocks in the radio due to shock re-acceleration.