Session 4: Our Galaxy and other galaxies

Title: Opacity of spiral galaxies.
Author: E. Xilouris  (Best PhD talk in Special Session)

We compare optical and near-infrared surface photometry of seven edge-on spiral galaxies with corresponding surface photometry calculated from a realistic model of spiral galaxies which takes into account both absorption and scattering by the interstellar dust. For the stars and the dust in the disk we use exponential distributions in both directions, radially and perpendicular to the plane of the disk, while the de Vaucouleurs profile is used for the description of the bulge. From this analysis we were able to determine all the parameters that best fit the surface photometry of the galaxies. The face-on central optical depth is calculated to be less than one in all optical bands and for all seven galaxies studied, indicating that typical spiral galaxies would be completely transparent if they were to be seen face-on. Recent far-infrared (ISO) and submillimeter (SCUBA) observations confirm the model predictions.