Angular momentum of disc galaxies with a lognormal density distribution

By postulating that the majority of the mass and angular momentum of a disc galaxy is confined to the disc with a lognormal surface density distribution, and that galactic discs are substantially, if not fully, self-gravitating, it may be shown that the resultant rotation curves (RCs) display a good overall fit to observational data for a wide range of galaxy types. With this hypothesis, the total angular momentum J, and total energy vertical bar E vertical bar of 38 disc galaxies was computed and plotted against the derived disc masses, with best fit slopes for J of 1.683 +/- 0.018 and vertical bar E vertical bar of 1.643 +/- 0.038, and a universal disc spin parameter lambda = 0.423 +/- 0.014. Using the disc parameters V-max and R-max as surrogates for the virial velocity and radius, a virial mass estimator M-disc alpha R-max V-max(2) was generated, with a log-log slope of 1.024 +/- 0.014 for the 38 galaxies, and a proportionality constant lambda* = 1.47 +/- 0.20 x 10(5) M-circle dot kpc(-1) km(-2) s(2). This relationship has less scatter than M alpha (V-rot)(alpha), and may provide an alternative to the Tully-Fisher relation in determining virial disc masses.