A Song of Shocks and Dynamo: Numerical Studies of a Galaxy Cluster Merger in the HIMAG Project

TL;DR

This study uses advanced ENZO simulations to explore magnetic field evolution, shock acceleration, and cosmic-ray electron cooling in galaxy cluster mergers, revealing the development of small-scale dynamos and radio emission mechanisms.

Contribution

First simulation to incorporate cosmic-ray electron cooling in modeling radio emission from galaxy clusters, demonstrating magnetic field amplification and shock acceleration processes.

Findings

Magnetic fields grow to microgauss levels during cluster formation.

Shock waves accelerate cosmic-ray electrons emitting radio waves.

Cosmic-ray electron cooling affects radio emission modeling.

Abstract

With ENZO simulations run on the J\"ulich supercomputers, we have investigated the evolution of magnetic fields in the largest cosmic structures (namely galaxy clusters and filaments connecting them) with unprecedented dynamical range. These simulations revealed the full development of the small-scale dynamo in Eulerian cosmological magneto-hydrodynamical simulations. The turbulent motions developed during the formation of clusters are energetic enough to foster the growth of magnetic fields by several orders of magnitude, starting from weak magnetic fields up strengths of $\sim \rm \mu G$ as observed. Furthermore, shock waves are launched during cluster formation and they are able to accelerate cosmic-ray electrons, that emit in the radio wavelengths. Radio observations of this emission provide information on the local magnetic field strength. We have incorporated, for the first time, the cooling of cosmic-ray electrons when modelling this emission. In this contribution, we present our advances in modelling these physical processes. Here, we mostly focus on the most interesting object in our sample of galaxy clusters, which shows the complexity of magnetic fields and the potential of existing and future multi-wavelengths observations in the study of the weakly collisional plasma on $\sim$ Megaparsecs scales.