THE NATURE OF S0 GALAXIES

It is tentatively suggested that SO galaxies belong to two (possibly o verlapping) populations. One of these contains mainly luminous oblate objects that are truly intermediate between ellipticals and spirals. T he other population of SO galaxies appears to consist of fainter, pred ominantly prolate objects. Evidence for this conclusion is based on th e observation that the luminosity function of SO galaxies appears to c ontain a faint component that is not, or only weakly, present among E and Sa galaxies. The objects belonging to this faint population have a distribution of apparent axial ratios that is even flatter than that observed for galaxies of type Sc. This suggests that this population o f faint flattened objects is mainly composed of predominantly prolate galaxies. Alternatively it might be assumed that SO galaxies, on avera ge, become more triaxial towards lower luminosities.