Gravitational Lensing by Dark Matter Halos with Nonuniversal Density Profiles

The statistics of gravitational lensing can provide us with a very powerfulprobe of the mass distribution of matter in the universe. By comparingpredicted strong lensing probabilities with observations, we can test the massdistribution of dark matter halos, in particular, the inner density slope. Inthis letter, unlike previous work that directly models the density profiles ofdark matter halos semi-analytically, we generalize the density profiles of darkmatter halos from high-resolution N-body simulations by means of generalizedNavarro-Frenk-White (GNFW) models of three populations with slopes, $\alpha$,of about -1.5, -1.3 and -1.1 for galaxies, groups and clusters, respectively.This approach is an alternative and independent way to examine the slopes ofmass density profiles of halos. We present calculations of lensingprobabilities using these GNFW profiles for three populations in variousspatially flat cosmological models with a cosmological constant $\Lambda$. Itis shown that the compound model of density profiles does not match well withthe observed lensing probabilities derived from the Jodrell-Bank VLAAstrometric Survey data in combination with the Cosmic Lens All-Sky Surveydata. Together with the previous work on lensing probability, our resultssuggest that a singular isothermal sphere mass model of less than about$10^{13}h^{-1}M_{\sun}$ can predict strong lensing probabilities that areconsistent with observations of small splitting angles.Comment: 11 pages, 2 figures, Accepted by ApJL for publication (February 10 issue 2004