MHD simulations of a supernova-driven ISM and the warm ionized medium using a positivity preserving ideal MHD scheme

TL;DR

This paper presents advanced 3D MHD simulations of the supernova-driven interstellar medium, demonstrating the impact of magnetic fields and domain size on gas distribution and ionization, with implications for understanding the warm ionized medium.

Contribution

It introduces a stable, positivity-preserving MHD scheme in simulations of the ISM, exploring magnetic effects and domain size to better match observed emission measures.

Findings

Magnetic fields influence the gas distribution and ionization structure.

The magnetic energy reaches a steady state after a few hundred million years.

Including magnetic fields improves the match to observed emission measure distributions.

Abstract

We present new 3D magnetohydrodynamic (MHD) simulations of a supernova-driven, stratified interstellar medium. These simulations were run using the Waagan (2009) positivity preserving scheme for ideal MHD implemented in the Flash code. The scheme is stable even for the Mach numbers approaching 100 found in this problem. We have previously shown that the density distribution arising from hydrodynamical versions of these simulations creates low-density pathways through which Lyman continuum photons can travel to heights |z| > 1 kpc. This naturally produces the warm ionized medium through photoionization due primarily to O stars near the plane. However, our earlier models reproduce the peak but not the width of the observed emission measure distribution. Here, we examine whether inclusion of magnetic fields and a greater vertical extent to the simulation domain produce a gas distribution that better matches the observations. We further study the change of magnetic energy over time in our models, showing that it appears to reach a steady state after a few hundred megayears, presumably supported by a turbulent dynamo driven by the supernova explosions.