  We investigate the formation of disk-bulge-halo systems by including bulges
in the Fall & Efstathiou theory of disk formation. This allows an investigation
of bulge dominated disk galaxies, such as S0s and disky ellipticals. The aim of
this paper is to examine whether spirals, S0s, and disky elllipticals all can
be incorporated in one simple galaxy formation scenario. We investigate an
inside-out formation scenario in which the inner, low angular momentum material
is assumed to form the bulge. Stability arguments are used to suggest that this
bulge formation is a self-regulating process in which the bulge grows until it
is massive enough to allow the remaining gas to form a stable disk component.
We search for the parameters and physical processes that determine the
disk-to-bulge ratio, and therewith explain to a large extent the origin of the
Hubble sequence. The spread in halo angular momenta coupled with a spread in
the formation redshifts can explain the observed spread in disk properties and
disk-to-bulge ratios from spirals to S0s. Disky ellipticals, however, are too
compact to be incorporated. Upon introducing a galaxy formation efficiency that
depends on redshift, as suggested by the small amount of scatter in the
observed Tully-Fisher relation, this scenario naturally predicts a
density-morphology relation, the amplitude of which depends on the baryon
fraction of the Universe.
