Ivana Beslic
LERMA, Observatoire de Paris
Investigating magnetic field properties across NGC 2024 in Orion B
The magnetic (B-) field supporting interstellar clouds against gravitational collapse could explain the low star formation efficiency observed in galaxies and the Milky Way. The Planck satellite has provided the first all-sky map of the B-field geometry in the diffuse interstellar medium. However, higher spatial resolution observations are necessary to understand better the transition from diffuse, non-collapsing gas to dense, gravitationally unstable filaments. NGC 2024 is in the nearby Orion B molecular cloud. It contains a young, expanding HII region and a dense supercritical filament hosting embedded protostellar objects. Therefore, NGC 2024 provides an excellent opportunity to study the role of B-fields in the formation, evolution, and collapse of dense filaments, the dynamics of young HII regions, and the effects of mechanical and radiative feedback from massive stars on the surrounding molecular gas. In Beslic+2024, we combine new 154 and 216 microns dust polarization measurements carried out using the HAWC+ instrument aboard SOFIA with molecular line observations of 12CN(1-0) and HCO+(1-0) from the IRAM 30-meter telescope to determine the B-field geometry and to estimate the plane of the sky B-field strength across the NGC 2024 HII region and the surrounding molecular cloud. The HAWC+ observations show an ordered B-field geometry in NGC 2024 that follows the morphology of the expanding HII region and the direction of the main dense filament. The derived plane of the sky B-field strength is moderate, ranging from 30 to 80 micro G. The strongest B-field is found at the northern-west edge of the HII region, characterized by the highest gas densities and molecular line widths. In contrast, the weakest field is found toward the main, dense filament in NGC 2024. The B-field has a non-negligible influence on the gas stability at the edges of the expanding HII shell (gas impacted by the stellar feedback) and the filament (site of the current star formation). Ref: Beslic et al., 2024, accepted for publication in A&A
