2002ApJ...565L...1S

Current data suggest that the central mass densities ρ₀ and phase-space densities Q≡ρ₀/σ³_V of cosmological halos in the present universe are correlated with their velocity dispersions σ_V over a very wide range of σ_V from less than 10 to more than 1000 km.s^–1. Such correlations are an expected consequence of the statistical correlation of the formation epochs of virialized objects in the cold dark matter (CDM) model with their masses; the smaller mass halos typically form first and merge to form larger mass halos later. We have derived the Q-σ_V and ρ₀-σ_V correlations for different CDM cosmologies and compared the predicted correlations with the observed properties of a sample of low-redshift halos ranging in size from dwarf spheroidal galaxies to galaxy clusters. Our predictions are generally consistent with the data, with preference for the currently favored, flat low-density CDM model with cosmological constant (ΛCDM). Such a comparison serves to test the basic CDM paradigm while constraining the background cosmology and the power spectrum of primordial density fluctuations, including larger wavenumbers than have previously been constrained.