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

a) Large scale view of NGC 3324 using a three-color composite map (SUMSS 843 MHz (in red), Herschel 160 µm (in green), and Herschel 70 µm (in blue) images). Squares show the locations of massive O-type stars. Boxes indicate areas which are examined in this work. A solid box emcomapsses an area presented in Figures A1b, A1c, and A1d. b) The panel shows a three-color composite map (Herschel 70 µm (in red), Spitzer 8.0 µm (in green), and Spitzer 3.6 µm (in blue) images in linear scale). The area of the image is ~8.'5 × 9.'8 (central coordinates: a2000 = 10h36m43.s25; d2000 = -58?37'12.''82). All the symbols are the same as presented in Figure 1a. The dust continuum clumps highlighted by stars are also labeled. c) Overlay of the SUMSS 843 MHz radio continuum contours on the CHaMP 13CO moment-0 map at [-24.3, -19.9] km s-1. The SUMSS 843 MHz radio continuum contours (see dotted-dashed contours) are plotted with the levels of 46.5, 62.3, 78, 94, 109, and 125 mJy beam-1. The SUMSS contours (see solid contours) are presented with the levels of 132, 141, 157, 172, 188, 204, and 212 mJy beam-1. d) Herschel dust temperature map. In panels “c” and “d”, a thick curve shows the footprint of the sharp edge as seen in Figure A1b. In panels “b”, “c” and “d”, a small region (i.e., “sm1”) is indicated by a small yellow box. Scale bars are shown (at 1000'' (or 10.7 pc at a distance of 2.2 kpc) and 120'' (or 1.28 pc)). 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 µm images (resolution ~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 ~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 µm polycyclic aromatic hydrocarbon (PAH) emission, the 4.05 µm ionized emission, and the 4.693 µm H2 emission. However, the PAH-emitting structures are depicted between the other two. The H2 emission reveals numerous intertwined sub-structures which are not prominently traced in the 3.3 µm PAH emission. The separation between two sub-structures in the H2 emission is ~1.1'' or 2420 AU. The intertwined sub-structures are traced in the spatial areas associated with the neutral to H2 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 µm images is investigated as a bipolar HII region (extent ~0.35 pc) at Td ~25-28~K using the JWST images. A massive star candidate VPHAS-OB1 #03518 seems to be responsible for the bipolar HII region.