Abstract

This work presents high-precision measurements of the specific baryon angular momentum j _b contained in stars, atomic gas, and molecular gas, out to >~ 10 scale radii, in 16 nearby spiral galaxies of the THINGS sample. The accuracy of these measurements improves on existing studies by an order of magnitude, leading to the discovery of a strong correlation between the baryon mass M _b, j _b, and the bulge mass fraction β, fitted by \beta =-(0.34+/- 0.03)\,lg\,(j_bM_b^{-1}/[10^{-7}\, kpc\,km\,s^{-1}\,{M}_{\odot }^{-1}])-(0.04+/- 0.01) on the full sample range of 0 <= β <~ 0.3 and 10⁹ M _☉ < M _b < 10¹¹ M _☉. The corresponding relation for the stellar quantities M _* and j _* is identical within the uncertainties. These M-j-β relations likely originate from the proportionality between jM ^-1 and the surface density of the disk that dictates its stability against (pseudo-)bulge formation. Using a cold dark matter model, we can approximately explain classical scaling relations, such as the fundamental plane of spiral galaxies, the Tully-Fisher relation, and the mass-size relation, in terms of the M-j(-β) relation. These results advocate the use of mass and angular momentum as the most fundamental quantities of spiral galaxies.