The large-scale properties of simulated cosmological magnetic fields

TL;DR

This paper uses large-scale cosmological simulations to study the evolution and properties of magnetic fields in the universe, revealing how feedback processes influence magnetic amplification and topology.

Contribution

It provides the first comprehensive analysis of magnetic field amplification and topology in cosmological simulations with different physics models, including feedback and cooling effects.

Findings

Magnetic field amplification follows flux-freezing scaling in adiabatic runs.

Feedback and cooling significantly alter magnetic field strength and structure.

Magnetic fields in galaxy clusters reach observed levels of 10-100 μG.

Abstract

We perform uniformly sampled large-scale cosmological simulations including magnetic fields with the moving mesh code AREPO. We run two sets of MHD simulations: one including adiabatic gas physics only; the other featuring the fiducial feedback model of the Illustris simulation. In the adiabatic case, the magnetic field amplification follows the $B \propto \rho^{2/3}$ scaling derived from `flux-freezing' arguments, with the seed field strength providing an overall normalization factor. At high baryon overdensities the amplification is enhanced by shear flows and turbulence. Feedback physics and the inclusion of radiative cooling change this picture dramatically. In haloes, gas collapses to much larger densities and the magnetic field is amplified strongly and to the same maximum intensity irrespective of the initial seed field of which any memory is lost. At lower densities a dependence on the seed field strength and orientation, which in principle can be used to constrain models of cosmic magnetogenesis, is still present. Inside the most massive haloes magnetic fields reach values of $\sim 10-100\,\,{\rm \mu G}$, in agreement with galaxy cluster observations. The topology of the field is tangled and gives rise to rotation measure signals in reasonable agreement with the observations. However, the rotation measure signal declines too rapidly towards larger radii as compared to observational data.