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

Recent JWST observations of HII regions in the Central Molecular Zone have shown a highly filamentary morphology distinct from HII regions in the solar neighborhood. We present magnetohydrodynamic (MHD) simulations, using the Athena++ simulation framework, of strongly magnetized (β ≪ 1) HII region evolution that effectively recreate the formation of these ionized gas filaments. HII region evolution has been simulated in a 30 pc 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. Given that these filaments are effectively magnetically-confined flows of photoionized gas, their density and curvature are determined by the density of the blob and the geometry of the configuration.