Galaxy morphology in rich clusters - Implications for the formation and evolution of galaxies

The paper presents a study of the galaxy populations in 55 rich clusters along with a discussion of the implications for the formation and/or evolution of different morphological types. A well defined relationship is found between local galaxy density and galaxy type, which indicates an increasing elliptical and S0 population and a corresponding decrease in spirals with increasing density. Attention is given to evidence which contradicts the interpretation that these gradients in population result from the production of S0 galaxies when spirals are swept of disk gas by an IGM. In addition, as an alternative to the hypothesis of spiral sweeping, it is suggested that the local density/morphological-type relation reflects the long time scale associated with the formation of the disk component of galaxies. Finally, the data also indicate a trend of increasing luminosity of the spheroidal component with increasing local density.