2018ApJ...868..133F

We show that the stellar specific angular momentum j_*, mass M_*, and bulge fraction β_* 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_^α^ and j_*b_∝M_*b_^α^ with α=0.67±0.07 but offset from each other by a factor of 8 ± 2 over the mass range 8.9≤ log(M_*/M_☉)≤ 11.8. Separate fits for disks and bulges alone give α=0.58±0.10 and α=0.83±0.16, respectively. This model correctly predicts that galaxies follow a curved 2D surface in the 3D space of logj_*, logM_*, and β_*. 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 β_* dependence of the j_*-M_* scaling relations. The results presented here reinforce and extend our earlier suggestion that the distribution of galaxies with different β_* in the j_*-M_* diagram constitutes an objective, physically motivated alternative to subjective classification schemes such as the Hubble sequence.