New insights in the bubble wall of NGC 3324: intertwined sub-structures and a bipolar morphology uncovered by JWST (2309.13351v1)

Abstract: We report the discovery of intertwined/entangled sub-structures towards the bubble wall of NGC 3324 below a physical scale of 4500 AU, which is the sharp edge/ionization front/elongated structure traced at the interface between the HII region and the molecular cloud. The sharp edge appears wavy in the Spitzer 3.6-8.0 $\mu$m images (resolution $\sim$2$''$). Star formation signatures have mostly been traced on one side of the ionization front, which lies on the molecular cloud's boundary. The James Webb Space Telescope's (JWST) near- and mid-infrared images (resolution $\sim$0.07$''$-0.7$''$) are employed to resolve the sharp edge, which has a curvature facing the exciting O-type stars. The elongated structures are associated with the 3.3 $\mu$m polycyclic aromatic hydrocarbon (PAH) emission, the 4.05 $\mu$m ionized emission, and the 4.693 $\mu$m H${2}$ emission. However, the PAH-emitting structures are depicted between the other two. The H${2}$ emission reveals numerous intertwined sub-structures which are not prominently traced in the 3.3 $\mu$m PAH emission. The separation between two sub-structures in the H${2}$ emission is $\sim$1.1$''$ or 2420 AU. The intertwined sub-structures are traced in the spatial areas associated with the neutral to H${2}$ transition zone, suggesting the origin of these structures by ``thin-shell'' instability. Furthermore, an arc-like feature traced in the Spitzer 3.6-8.0 $\mu$m images is investigated as a bipolar HII region (extent $\sim$0.35 pc) at T$_\mathrm{d}$ $\sim$25-28~K using the JWST images. A massive star candidate VPHAS-OB1 #03518 seems to be responsible for the bipolar HII region.