A simple model for the clustering of subhalos as a function of mass

Abstract

Astrophysicists do not associate galaxies with the massive dark matter halos so easily detected in particle simulations and whose mass function can be predicted by the Press-Schechter formalism and its variants. Instead, they associate galaxies with smaller surviving subhalos whose contents do not fully mix into the larger dark matter halos they exist in. However, these subhalos are as of now difficult to find in simulations. I present a simple description of what the Press-Schechter formalism can say about the clustering of these subhalos, under the restrictive assumption that at fixed subhalo mass, the chance of survival of the subhalo is independent of its larger scale environment. This model predicts a weak dependence of clustering on mass below masses of about 10^12 solar masses, in agreement with observations of a weak dependence of clustering on luminosity at luminosities less than L*. The model is in qualitative agreement with observations that at low luminosities galaxy clustering is a strong function of color while at high luminosities galaxy clustering is a strong function of luminosity.