Global Dynamical Evolution of the ISM in Star Forming Galaxies - I. High Resolution 3D HD and MHD Simulations: Effect of the Magnetic Field

TL;DR

This study uses high-resolution 3D MHD simulations to explore how magnetic fields influence matter circulation and phase structure in the interstellar medium of star-forming galaxies, revealing that magnetic fields delay but do not prevent gas transport into the halo.

Contribution

It provides detailed 3D MHD simulation results on the role of magnetic fields in the ISM dynamics and matter circulation in star-forming galaxies, with high spatial resolution and long simulation times.

Findings

Magnetic fields delay but do not prevent gas transport into the halo.

The hot phase volume filling factor is similar in HD and MHD runs (~17-21%).

Magnetic fields influence the phase structure but do not significantly alter the hot gas volume fraction.

Abstract

In star forming disk galaxies, matter circulation between stars and the interstellar gas, and, in particular the energy input by random and clustered supernova explosions, determine the dynamical and chemical evolution of the ISM, and hence of the galaxy as a whole. Using a 3D MHD code with adaptive mesh refinement developed for this purpose, we have investigated the r\^ole of magnetized matter circulation between the gaseous disk and the surrounding galactic halo. Special emphasis has been put on the effect of the magnetic field with respect to the volume and mass fractions of the different ISM ``phases'', the relative importance of ram, thermal and magnetic pressures, and whether the field can prevent matter transport from the disk into the halo. The simulations were performed on a grid with an area of 1 kpc$^{2}$, centered on the solar circle, extending $\pm 10$ kpc perpendicular to the galactic disk with a resolution as high as 1.25 pc. The simulations were run for a time scale of 400 Myr, sufficiently long to avoid memory effects of the initial setup, and to allow for a global dynamical equilibrium to be reached in case of a constant energy input rate. (...) We find that in general gas transport into the halo in 3D is not prevented by an initial disk parallel magnetic field, but only delayed initially, for as long as it is needed to punch holes into the thick magnetized gas disk. The mean volume filling factor of the hot phase in the disk is similar in HD and MHD (the latter with a total field strength of 4.4 $\mu$G) runs, amounting to $\sim 17-21%$ for the Galactic supernova rate.