MHD Simulations of Strongly Magnetized HII Region Evolution: Evidence for Ionized Gas Filamentation

TL;DR

This study uses MHD simulations to explore how strong magnetic fields influence the formation of filamentary structures in ionized gas regions, matching recent JWST observations of the Galactic Center.

Contribution

It demonstrates that pre-existing overdensities in a magnetized medium lead to filament formation aligned with magnetic fields during HII region evolution.

Findings

Ionized gas filaments are formed along magnetic field lines.

Filament properties match those observed in the Central Molecular Zone.

Magnetic confinement influences filament density and shape.

Abstract

Recent JWST observations of HII regions in the Central Molecular Zone have shown a highly filamentary morphology distinct from HII regions in other parts of the galaxy. We present magnetohydrodynamic (MHD) simulations of strongly magnetized (plasma-$\beta$ << 1) HII region evolution that investigate and describe the formation of these ionized gas filaments. HII region evolution has been simulated in a 30 pc$^3$ box, in distinct models with pre-placed overdensities in the ambient medium and overdensities that have been generated with driven turbulence. We find that when these overdensities are seeded in the ambient medium before the birth of the ionizing source, the photoionized plasma stripped off of these dense blobs is funneled into long filaments along the magnetic field lines. The length and emission measure of these ionized gas filaments are similar to the filaments observed in the Central Molecular Zone. Given that these filaments are effectively magnetically-confined flows of photoionized gas, their density and curvature are influenced by the density of the blob and the geometry of the configuration.