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New insights in the bubble wall of NGC 3324: intertwined sub-structures and a bipolar morphology uncovered by JWST Published: 9/23/2023 3:01:40 PM Updated: 9/23/2023 3:01:40 PM

Paper abstract: We report the discovery of intertwined/entangled sub-structures towards thebubble wall of NGC 3324 below a physical scale of 4500 AU, which is the sharpedge/ionization front/elongated structure traced at the interface between theHII region and the molecular cloud. The sharp edge appears wavy in the Spitzer3.6-8.0 \mum images (resolution ~2''). Star formation signatures havemostly been traced on one side of the ionization front, which lies on themolecular cloud's boundary. The James Webb Space Telescope's (JWST) near- andmid-infrared images (resolution ~0.07''-0.7'') are employed to resolvethe sharp edge, which has a curvature facing the exciting O-type stars. Theelongated structures are associated with the 3.3 \mum polycyclic aromatichydrocarbon (PAH) emission, the 4.05 \mum ionized emission, and the 4.693\mum H_{2} emission. However, the PAH-emitting structures are depictedbetween the other two. The H_{2} emission reveals numerous intertwinedsub-structures which are not prominently traced in the 3.3 \mum PAH emission.The separation between two sub-structures in the H_{2} emission is~1.1'' or 2420 AU. The intertwined sub-structures are traced in thespatial 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 \mum images isinvestigated as a bipolar HII region (extent ~0.35 pc) at T_\mathrm{d}~25-28~K using the JWST images. A massive star candidate VPHAS-OB1 #03518seems to be responsible for the bipolar HII region.