Dynamically dominant magnetic fields in the diffuse interstellar medium

TL;DR

This paper investigates how magnetic fields in the diffuse interstellar medium can become detached from dense clouds, resulting in a magnetically dominated diffuse gas, through theoretical, modeling, and simulation approaches.

Contribution

It introduces a combined theoretical, modeling, and simulation framework to demonstrate magnetic flux shedding from forming dense clouds in the ISM.

Findings

Magnetic flux can be significantly shed during cloud formation.

Diffuse gas remains magnetically dominated after cloud formation.

Magnetic fields do not always respond to gas density increases as expected.

Abstract

Observations show that magnetic fields in the interstellar medium (ISM) often do not respond to increases in gas density as would be naively expected for a frozen-in field. This may suggest that the magnetic field in the diffuse gas becomes detached from dense clouds as they form. We have investigated this possibility using theoretical estimates, a simple magneto-hydrodynamic model of a flow without mass conservation and numerical simulations of a thermally unstable flow. Our results show that significant magnetic flux can be shed from dense clouds as they form in the diffuse ISM, leaving behind a magnetically dominated diffuse gas.