Angular Momentum and Galaxy Formation Revisited: Scaling Relations for Disks and Bulges

Understand

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_*.