Which galaxy property is the best indicator of its host dark matter halo properties?

Abstract

In this work we investigate the link between galaxy velocity dispersion, mass and other properties (color, morphology) with the properties of dark matter halos by comparing the clustering of galaxies at both fixed mass and velocity dispersion. We use the Sloan Digital Sky Survey to define a volume limited sample of massive galaxies complete in both stellar mass (>6e10 Msun) and velocity dispersion (>75 km/s). Using this sample we show that at fixed velocity dispersion there is no dependence of the clustering amplitude on stellar or dynamical mass. Conversely when stellar or dynamical mass are fixed there is a clear dependence of the clustering amplitude on velocity dispersion with higher dispersion galaxies showing a higher clustering amplitude. We also show that whilst when stellar or dynamical mass are fixed there remains a dependence of clustering amplitude on morphology, there is no such dependency when dispersion is fixed. However, we do see a dependence of the clustering amplitude on color when both mass and dispersion are fixed. Despite this, even when we restrict our samples to only elliptical or red galaxies the relationship between dispersion and clustering amplitude at fixed mass remains. It seems likely that the residual correlation with color is driven by satellite galaxies in massive halos being redder at fixed dispersion. The lack of a similar morphology dependence implies that the mechanism turning satellites red is not changing their morphology. Our central result is that velocity dispersion is more closely related to the clustering amplitude of galaxies than either stellar or dynamical mass. This implies that velocity dispersion is more tightly correlated with the halo properties that determine clustering, either halo mass or age, and supports the notion that the star formation history of a galaxy is more closely related to its halo properties than its overall mass.