James Webb Space Telescope Feed Post

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

Multi-wavelength view of an area “sm1” as indicated by a solid box in Figure 1a. a–e) JWST images at F187N, F200W, F335M, F770W, and F1130W are displayed, respectively. f) The panel shows a three-color composite map (F1130W (in red), F770W (in green), and F335W (in blue) images in linear scale). g) F470N-F444W (in linear scale). h) F444W/F335M (in linear scale). i) The panel presents a two-color composite map (F444W/F335M (red) and F470N-F444W (turquoise) images in linear scale). In panels “c”, “d”, and “g”, an arrow shows the position of an OB-star candidate (UCAC4 157-048728 or VPHAS-OB1 #03518; Mohr-Smith et al. 2017). In panel “g”, three H2 depression regions (i.e, CC-1, CC-2, and CC-3) and one emission structure (FF-1) are labeled. In panel “i”, a bipolar morphology is highlighted, and the position of the OB-star candidate UCAC4 157-048728 is found at its waist. In each panel, a scale bar corresponding to 20'' (or 0.21 pc at a distance of 2.2 kpc) is drawn. 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.