The velocity dispersion function of early-type galaxies

The distribution of early-type galaxy velocity dispersions, phi(sigma), is measured using a sample drawn from the Sloan Digital Sky Survey database. Its shape differs significantly from that obtained by simply using the mean correlation between luminosity L and velocity dispersion sigma to transform the luminosity function into a velocity function: ignoring the scatter around the mean sigma-L relation is a bad approximation. An estimate of the contribution from late-type galaxies is also made, which suggests that phi(sigma) is dominated by early-type galaxies at velocities larger than similar to 200 km s(-1).