Turbulent Amplification and Structure of the Intracluster Magnetic Field

TL;DR

This paper compares turbulence simulations with intra-cluster turbulence data to evaluate magnetic dynamo action, revealing that magnetic fields in galaxy clusters reflect their turbulent history and are consistent with observations.

Contribution

It introduces a method to normalize dynamo action using intra-cluster turbulence data, overcoming low Reynolds number limitations in current models.

Findings

Magnetic field properties are insensitive to seed field variations.

Resulting Alfven speeds and outer scales match observational estimates.

Magnetic fields record the turbulent history of galaxy clusters.

Abstract

We compare DNS calculations of homogeneous isotropic turbulence with the statistical properties of intra-cluster turbulence from the Matryoshka Run (Miniati 2014) and find remarkable similarities between their inertial ranges. This allowed us to use the time dependent statistical properties of intra-cluster turbulence to evaluate dynamo action in the intra-cluster medium, based on earlier results from numerically resolved nonlinear magneto-hydrodynamic turbulent dynamo (Beresnyak 2012). We argue that this approach is necessary (a) to properly normalize dynamo action to the available intra-cluster turbulent energy and (b) to overcome the limitations of low Re affecting current numerical models of the intra-cluster medium. We find that while the properties of intra-cluster magnetic field are largely insensitive to the value and origin of the seed field, the resulting values for the Alfven speed and the outer scale of the magnetic field are consistent with current observational estimates, basically confirming the idea that magnetic field in today's galaxy clusters is a record of its past turbulent activity.