The Velocity Dispersion Function of Early-Type Galaxies

The distribution of early-type galaxy velocity dispersions,φ(σ), is measured using a sample drawn from the Sloan DigitalSky Survey database. Its shape differs significantly from that obtainedby simply using the mean correlation between luminosity L and velocitydispersion σ to transform the luminosity function into a velocityfunction: ignoring the scatter around the mean σ-L relation is abad approximation. An estimate of the contribution from late-typegalaxies is also made, which suggests that φ(σ) is dominatedby early-type galaxies at velocities larger than ~200 km s^-1.