3D MHD simulations of magnetic field evolution and radio polarization of barred galaxies

Aims. We study numerically the large-scale gas and magnetic field evolution of barred galaxies in the gravitational potential of a disk, bulge, halo, and bar. We solve non-linear MHD equations including the back-reaction of the magnetic field to the gas. We do not take into account any dynamo process. Methods. We apply the numerical MHD code to calculate the model of the galaxy in three dimensions. We construct realistic maps of high-frequency (Faraday rotation free) polarized radio emission on the basis of the simulated magnetic fields. The polarization model includes the effects of projection and limited resolution. Results. The main result is that our modeled polarization maps resemble the radio polarization structures observed in barred galaxies. The modeled polarization B-vectors distribution along the bar and between spiral arms resembles the observed topology of the magnetic field in barred galaxies. Our calculations for several different rotational velocities and sound speeds give the same result we got in our previous earlier published model. The reason of this behaviour is the dynamical evolution of the bar that causes gas to form spiral waves going radially outward. A gaseous spiral arms in turn generates magnetic ones, which live much longer in the inter-arm disk space than the gaseous pattern

Cosmic ray driven dynamo in barred and ringed galaxies

We study the global evolution of the magnetic field and interstellar medium (ISM) of the barred and ringed galaxies in the presence of non-axisymmetric components of the potential, i.e. the bar and/or the oval perturbations. The magnetohydrodynamical dynamo is driven by cosmic rays (CR), which are continuously supplied to the disk by supernova (SN) remnants. Additionally, weak, dipolar and randomly oriented magnetic field is injected to the galactic disk during SN explosions. To compare our results directly with the observed properties of galaxies we construct realistic maps of high-frequency polarized radio emission. The main result is that CR driven dynamo can amplify weak magnetic fields up to few $\mu$G within few Gyr in barred and ringed galaxies. What is more, the modelled magnetic field configuration resembles maps of the polarized intensity observed in barred and ringed galaxies

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

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