ON THE TRANSPARENCY OF THE INNER REGIONS OF EARLY-TYPE SPIRAL GALAXIES

Surface photometry of 17 inclined Sa-Sb galaxies with prominent bulges from the ESO-LV Data Base has been analyzed with the aim of detecting the possible effects of a hypothetical absorbing layer bisecting the central bulge. Our method is based on looking for an asymmetry between the photometric profiles of the two semi-minor axes, and is complementary to the surface brightness-inclination test which, for early spirals with bright bulges, is confused by the very presence of these bulges. None of the galaxies in our sample shows evidence of a continuous, near-opaque layer reaching the very center. Our conclusions are strengthened by two additional, well-studied objects, M 31 and M 104; our results indicate a lower obscuration in the central regions of early spirals with strong bulges compared to later types, and contribute to discriminate between competing models of light obscuration within galactic disks.