We show that the stellar specific angular momentum j _ { \star } , mass M _ { \star } , and bulge fraction \beta _ { \star } 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 _ { \star { d } } \propto M _ { \star { d } } ^ { \alpha } and j _ { \star { b } } \propto M _ { \star { b } } ^ { \alpha } with \alpha = 0.67 \pm 0.07 but offset from each other by a factor of 8 \pm 2 over the mass range 8.9 \leq \log ( M _ { \star } / M _ { \odot } ) \leq 11.8 .
Separate fits for disks and bulges alone give \alpha = 0.58 \pm 0.10 and \alpha = 0.83 \pm 0.16 , respectively .
This model correctly predicts that galaxies follow a curved 2D surface in the 3D space of \log j _ { \star } , \log M _ { \star } , and \beta _ { \star } .
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 _ { \star } – M _ { \star } 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 _ { \star } -dependence of the j _ { \star } – M _ { \star } scaling relations .
The results presented here reinforce and extend our earlier suggestion that the distribution of galaxies with different \beta _ { \star } in the j _ { \star } – M _ { \star } diagram constitutes an objective , physically motivated alternative to subjective classification schemes such as the Hubble sequence .