Flat rotation curves and mass distribution for spiral galaxies with a disk model

A method to fit flat rotation curves is presented, wherein the galactic density for a disk model is expressed in terms of a Dirichlet polynomial. This procedure allows us to obtain the total galactic mass and to predict the circular velocity at large galactocentric distances.Application of the method to the Galaxy, M31 and four Sc galaxies shows that a significant galactic mass is located beyond the optical radius although it is considerably smaller than the integral mass values obtained from current models with a massive corona included. Observed rotation curves and convergent total mass are obtained, thus the total mass for the Milky Way Galaxy is 5.69×10¹¹ M .