Shapley-ames Galaxies in the Blue and Infrared

The Shapley-Ames Catalog of 1276 galaxies with B < 12.5 is compared with the Sanders et al. all sky sample of the 629 galaxies with 60 μm flux density > 5.24 Jy. The fraction of Shapley-Ames galaxies that are visible in the IR is found to increase from 0.006 for E and E/S0 galaxies to 0.384 for Sc galaxies. The subset of Shapley-Ames galaxies that are detected in the IR has a median blue luminosity that is ∼0.8 mag fainter than that of all Shapley-Ames galaxies. Most of this difference is due to the fact that late-type galaxies (which contain dust and hot stars) are systematically less luminous in blue light than are earlytype galaxies. Within individual stages along the Hubble sequence no significant differences are found between the luminosity distributions in blue light of galaxies that were detected in the infrared and those that were not. However, our data show a puzzling exception (significant at 99.9% ) for SBc galaxies. For reasons that are not understood Shapley-Ames SBc galaxies, that are visible in the IR, are more luminous in blue light than those SBc galaxies that are not detected in the infrared. An other peculiarity of the data is that Shapley-Ames Sc galaxies galaxies are (at 99.6% confidence) more luminous in blue light than objects of type SBc. Subject headings: galaxies: statistics-galaxies: spiral