The Disc Contribution to Rotation Curves of Spiral Galaxies

We formulate analytically the maximum disc hypothesis (MDH) in the framework of a disc/halo mass decomposition, and apply it to a sample of suitably selected optical rotation curves. We find that the resulting disc-to-total mass ratios show a definite trend of increasing dark-to-luminous mass ratio with decreasing luminosity, in very good agreement with our previous results obtained by means of different decomposition techniques (Persic & Salucci). The same trend is also clearly discernible when the mass ratios (at the same radius in disc length-scale units) obtained from published MDH models are correlated with luminosity. We discuss possible reasons why previous studies which have assumed a similar framework have missed this fundamental systematics of dark matter.