The mass of dark matter in galaxies estimated from measurements of the velocities of light matter

The shape of rotation curves obtained for disc galaxies from Doppler measurements cannot per se provide information on the presence of dark nonbaryonic matter in those galaxies. The analysis of velocity dispersion of old discs of stars, however, together with photometric data allows for the disc-to-halo mass ratios to be estimated. These estimates yield a great deal of nonluminous mass in galaxies and allow for the possibility of studying the dynamical evolution of the discs of stars.