Mass-to-Light Ratios of Galaxies

Various methods for determining mass-to-light ratios are reviewed in [Tri87]. For the visible portions of normal elliptical galaxies M / L probably lies in the range 7 to 20 [Ba85, JF85]. The situation for spiral galaxies is more problematic because of their flat rotation curves extending (unconstrained) to radii where no further light is detected, at which point values of M / L ~ 25 are derived. Spiral galaxies with substantially lower M / L ratios may have experienced recent bursts of star formation; high values can occur in disk galaxies in quiescent phases of star formation.