Abstract:
We report the discovery of intertwined/entangled substructures toward 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 H II 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 substructures that are not prominently traced
in the 3.3 μm PAH emission. The separation between two substructures in the H2 emission is ∼1 1 or 2420 au.
The intertwined substructures 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 H II 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 H II region.
