The Velocity Dispersion Function for Quiescent Galaxies in the Local Universe

Abstract

We investigate the distribution of central velocity dispersions for quiescent galaxies in the SDSS at 0.03 <= z <= 0.10. To construct the field velocity dispersion function (VDF), we construct a velocity dispersion complete sample of quiescent galaxies with D(n)4000 > 1.5. The sample consists of galaxies with central velocity dispersion larger than the velocity dispersion completeness limit of the SDSS survey. Our VDF measurement is consistent with previous field VDFs for sigma > 200 km s(-1). In contrast with previous results, the VDF does not decline significantly for sigma < 200 km s(-1). The field and the similarly constructed cluster VDFs are remarkably flat at low velocity dispersion (sigma < 250 km s(-1)). The cluster VDF exceeds the field for sigma > 250 km s(-1) providing a measure of the relatively larger number of massive subhalos in clusters. The VDF is a probe of the dark matter halo distribution because the measured central velocity dispersion may be directly proportional to the dark matter velocity dispersion. Thus the VDF provides a potentially powerful test of simulations for models of structure formation.