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Session 63 - First Results from the Infrared Space Observatory.
Display session, Wednesday, June 12
We present 7 and 15 \mum images of NGC 6946 taken with the CAM instrument on ISO. This is the first CAM data from our ``US Key Project'' (Helou et al. 1996), which uses ISO LWS, CAM and PHOT observations to study ISM properties in normal galaxies. NGC 6946 is a nearby flocculent spiral galaxy with mostly normal star-formation pattern that peaks very strongly near the nucleus. The images were taken with a resolution of 6 \arcsec, corresponding to 300 pc for an assumed distance to NGC 6946 of 10 Mpc.
The emission at 7 \mum is believed to be dominated by PAHs (Polycyclic Aromatic Hydrocarbons), and the 15 \mum emission is primarily from the stochastically heated VSG (Very Small Grains) and very hot dust very near HII regions. The mid-infrared maps of NGC 6946 at both wavelengths clearly trace the spiral structure, and resolve structure therein. They will allow us to study in detail the spatial distribution of these emission components and their relation to spiral arms and HII regions. The ratio of 7 to 15 \mum maps will trace the relative strength of the two emission mechanisms, and may well yield a measure of the hardness of the heating spectrum in various parts of the galaxy.
Program listing for Wednesday