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A model for the CII and FIR emission in NGC 6946

S. Sauty , M. Gérin , & F. Casoli

DEMIRM, Observatoire de Paris, France Radioastronomie Millimétrique, Ecole Normale Supérieure, Paris, France

We present numerical simulations of radiative transfer in the spiral galaxy NGC 6946. It is possible to obtain a consistent picture of this galaxy with a global star formation rate of 4 M $_\odot$ yr^-1 (for stars with masses in the range 2-60 M $_\odot$ ) occuring mostly in the spiral arms. The close spatial association of massive stars and molecular clouds has a profound impact on the transfer of UV radiation in the galactic disk and on the dust and gas emission.

For radii less than 4 kpc, the C⁺ 158 $\mu m$ line is mostly produced in photodissociation regions at the surfaces of molecular clouds. The C⁺ emission from diffuse atomic gas accounts for about 20% of the total. It becomes significant at large distance from the nucleus ( $r \geq 4$ kpc). Molecular clouds and diffuse atomic gas have almost equal contributions to the total far infrared emission from 60 to 200 $\mu m$ . As a whole, 72% of the 60 - 200 $\mu m$ FIR emission can be attributed to dust grains heated by the UV radiation of massive stars and 28% by the radiation field of the old stellar population.

Next: The striking mid-infrared spectrum Up: Poster session E Galaxies Previous: ISO LWS observations of

"The Universe as seen by ISO", 20 - 23 October 1998, Paris: Abstract Book