Angular Momentum and Galaxy Formation Revisited: Scaling Relations for
  Disks and Bulges
  We show that the stellar specific angular momentum j_*, mass M_*, and bulge
fraction beta_* of normal galaxies of all morphological types are consistent
with a simple model based on a linear superposition of independent disks and
bulges. In this model, disks and bulges follow scaling relations of the form
j_*d ~ M_*d^alpha and j_*b ~ M_*b^alpha with alpha = 0.67 +/- 0.07 but offset
from each other by a factor of 8 +/- 2 over the mass range 8.9 <= log M_*/M_Sun
<= 11.8. Separate fits for disks and bulges alone give alpha = 0.58 +/- 0.10
and alpha = 0.83 +/- 0.16, respectively. This model correctly predicts that
galaxies follow a curved 2D surface in the 3D space of log j_*, log M_*, and
beta_*. We find no statistically significant indication that galaxies with
classical and pseudo bulges follow different relations in this space, although
some differences are permitted within the observed scatter and the inherent
uncertainties in decomposing galaxies into disks and bulges. As a byproduct of
this analysis, we show that the j_*--M_* scaling relations for disk-dominated
galaxies from several previous studies are in excellent agreement with each
other. In addition, we resolve some conflicting claims about the
beta_*-dependence of the j_*--M_* scaling relations. The results presented here
reinforce and extend our earlier suggestion that the distribution of galaxies
with different beta_* in the j_*--M_* diagram constitutes an objective,
physically motivated alternative to subjective classification schemes such as
the Hubble sequence.
