Turbulence and Dynamo in Galaxy Cluster Medium: Implications on the Origin of Cluster Magnetic Fields

TL;DR

This paper uses cosmological MHD simulations to demonstrate that magnetic fields ejected by AGNs can be transported and amplified by turbulence during galaxy cluster formation, potentially explaining the origin of cluster-wide magnetic fields.

Contribution

It provides the first self-consistent simulation showing AGN-ejected magnetic fields are amplified by ICM turbulence, leading to widespread cluster magnetic fields.

Findings

AGN ejected magnetic fields are transported throughout the cluster.

ICM turbulence, generated by mergers, amplifies magnetic fields.

A cluster-wide dynamo process amplifies magnetic energy to ~10^{61} ergs.

Abstract

We present self-consistent cosmological magnetohydrodynamic (MHD) simulations that simultaneously follow the formation of a galaxy cluster and the magnetic field ejection by an active galactic nucleus (AGN). We find that the magnetic fields ejected by the AGNs, though initially distributed in relatively small volumes, can be transported throughout the cluster and be further amplified by the intra-cluster medium (ICM) turbulence during the cluster formation process. The ICM turbulence is shown to be generated and sustained by the frequent mergers of smaller halos. Furthermore, a cluster-wide dynamo process is shown to exist in the ICM and amplify the magnetic field energy and flux. The total magnetic energy in the cluster can reach $\sim$ $10^{61}$ ergs while micro Gauss ($\mu$G) fields can distribute over $\sim$ Mpc scales throughout the whole cluster. This finding shows that magnetic fields from AGNs, being further amplified by the ICM turbulence through small-scale dynamo processes, can be the origin of cluster-wide magnetic fields.