Global simulations of the magnetic field evolution under the influence of the cosmic-ray-driven dynamo

TL;DR

This study uses 3D simulations to demonstrate that cosmic-ray-driven dynamo processes can amplify magnetic fields in barred galaxies to observed levels within a few billion years, producing realistic magnetic structures and polarization patterns.

Contribution

It introduces a detailed 3D simulation model showing how cosmic rays drive magnetic field amplification and structure formation in barred galaxies, aligning with observed properties.

Findings

Magnetic fields reach a few microGauss within 4 Gyr.

The dynamo amplifies initial weak fields with a 300 Myr e-folding time.

Modeled magnetic structures resemble observed polarized radio maps.

Abstract

We present three-dimensional global numerical simulations of the cosmic-ray (CR) driven dynamo in barred galaxies. We study the evolution of the interstellar medium of the barred galaxy in the presence of non-axisymmetric component of the potential, i.e., the bar. The magnetohydrodynamical dynamo is driven by CRs, which are continuously supplied to the disk by supernova (SN) remnants. No magnetic field is present at the beginning of simulations but one-tenth of SN explosions is a source of a small-scale randomly oriented dipolar magnetic field. In all models we assume that 10% of 10^51 erg SN kinetic energy output is converted into CR energy. To compare our results directly with the observed properties of galaxies, we construct realistic maps of polarized radio emission. The main result is that the CR-driven dynamo can amplify weak magnetic fields up to a few {\mu}G within a few Gyr in barred galaxies. The obtained e-folding time is equal to 300 Myr and the magnetic field reaches equipartition at time t ~ 4.0 Gyr. Initially, the completely random magnetic field evolves into large-scale structures. An even (quadrupole-type) configuration of the magnetic field with respect to the galactic plane can be observed. Additionally, the modeled magnetic field configuration resembles maps of the polarized intensity observed in barred galaxies. Polarization vectors are distributed along the bar and between spiral arms. Moreover, the drift of magnetic arms with respect to the spiral pattern in the gas density distribution is observed during the entire simulation time.