Formation of gaseous arms in barred galaxies with dynamically important magnetic field : 3D MHD simulations

TL;DR

This study uses 3D MHD simulations to explore how large-scale magnetic fields form and evolve in barred galaxies, revealing magnetic structures that match observed polarized radio emissions and explaining magnetic-velocity configuration discrepancies.

Contribution

The paper presents the first 3D MHD simulations of barred galaxies that include magnetic field back reaction and produce polarization maps consistent with observations, without relying on dynamo processes.

Findings

Magnetic field configurations resemble observed polarized intensity maps.

Gaseous spiral arms are accompanied by magnetic counterparts in inter-arm regions.

Magnetic energy grows constantly due to bar-induced compression and shear.

Abstract

We present results of three-dimensional nonlinear MHD simulations of a large-scale magnetic field and its evolution inside a barred galaxy with the back reaction of the magnetic field on the gas. The model does not consider the dynamo process. To compare our modeling results with observations, we construct maps of the high-frequency (Faraday-rotation-free) polarized radio emission on the basis of simulated magnetic fields. The model accounts for the effects of projection and the limited resolution of real observations. We performed 3D MHD numerical simulations of barred galaxies and polarization maps. The main result is that the modeled magnetic field configurations resemble maps of the polarized intensity observed in barred galaxies. They exhibit polarization vectors along the bar and arms forming coherent structures similar to the observed ones. In the paper, we also explain the previously unsolved issue of discrepancy between the velocity and magnetic field configurations in this type of galaxies. The dynamical influence of the bar causes gas to form spiral waves that travel outwards. Each gaseous spiral arm is accompanied by a magnetic counterpart, which separates and survives in the inter-arm region. Because of a strong compression, shear of non-axisymmetric bar flows and differential rotation, the total energy of modeled magnetic field grows constantly, while the azimuthal flux grows slightly until $0.05\Gyr$ and then saturates.