James Webb Space Telescope Feed Post

JWST Observations of Starbursts: Polycyclic Aromatic Hydrocarbon Emission at the base of the M 82 Galactic Wind

Comparison of different tracers of extra-planar material. A 5'' scale corresponds to 87.3 pc at the distance of M 82. Top left: Jansky VLA 6 GHz continuum at 0.36'' (6.3 pc) resolution (square root stretch, units MJy/sr). Top right: HST archival continuum-subtracted Paschen a at 0.25'' (4.4 pc) resolution (square root stretch, units erg s-1 cm-2 sr-1). Bottom left: NOEMA CO 1 - 0 peak intensity from Krieger et al. (2021) at 1.85'' (32.3 pc) resolution (linear stretch, units K). Bottom right: JWST 3.3 µm PAH emission at 0.11'' (1.9 pc) resolution (square root stretch, units MJy/sr). The ratio of 6 GHz to Paschen a implies the extra-planar filamentary radio continuum emission is thermal (see §3.2) The PAH emission shows very good detailed correspondence with the ionized gas traced by Paschen a and the radio continuum. A faint grid is superimposed to facilitate comparison. Abstract: We present new observations of the central 1 kpc of the M 82 starburst obtained with the James Webb Space Telescope (JWST) near-infrared camera (NIRCam) instrument at a resolution ~0.05"-0.1" (~1-2 pc). The data comprises images in three mostly continuum filters (F140M, F250M, and F360M), and filters that contain [FeII] (F164N), H2 v=1-0 (F212N), and the 3.3 um PAH feature (F335M). We find prominent plumes of PAH emission extending outward from the central starburst region, together with a network of complex filamentary substructure and edge-brightened bubble-like features. The structure of the PAH emission closely resembles that of the ionized gas, as revealed in Paschen alpha and free-free radio emission. We discuss the origin of the structure, and suggest the PAHs are embedded in a combination of neutral, molecular, and photoionized gas.