New perspectives on galactic angular momentum, galaxy formation, and the Hubble Sequence

This paper provides a summary of our recent work on the scaling relations between the specific angular momentum j_* and mass M_* of the stellar parts of normal galaxies of different bulge fraction beta_*. We find that the observations are consistent with a simple model based on a linear superposition of disks and bulges that follow separate 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. This model correctly predicts that galaxies follow a curved 2D surface in the 3D space of log j_, log M_, and beta_.