Galaxy formation: some comparisons between theory and observation

As a first approximation, it is reasonable to suppose that galaxies of a given disc-to-bulge ratio or morphological type form a sequence with mass as the fundamental parameter. The comparison of theory with data is further simplified by considering the extreme cases of ellipticals, with D/B << 1, and late-type spirals, with D/B >> 1. The approach outlined here is to explore the consequences of relaxing in succession the constraints that E, J and M be conserved during the collapse of proto-galaxies. The author concentrates on theories that are based on some form of hierarchical clustering: (1) E, J and M conserved; (2) E dissipated and J and M conserved; (3) E dissipated and J and M stripped. (Auth.)