THE TRANSFER OF RADIATION IN GALACTIC NUCLEI - DUSTY HOT-SPOTS IN THE STARBURST GALAXY M-82

We compute the equations of radiative transfer for the nucleus of a galaxy assuming that the dust is heated by stars. The stars are distributed over a wide volume of the nucleus. It is an important aspect of our model that dust temperatures vary not only on a galactic scale, but change also locally in the hot spots around luminous OB stars. Because of the often copious UV radiation field in a galactic nucleus and observational evidence in starburst galaxies we also consider in our model the presence of small grains and polycyclic aromatic hydrocarbons (PAHs) which both undergo temperature fluctuations and therefore strongly influence the near and mid IR part of the spectrum. We demonstrate the deficiency of those approximations which neglect either the hot spots or the emission by small grains or treat the stars as a point source located in the center of the galactic nucleus. Our method is applied to the starburst galaxy M 82. The overall spectrum, including PAH feautres is fitted as well as the observed source sizes between near IR to millimetre wavelengths.