Authors: David Merritt, Alister W. Graham, Ben Moore, Juerg Diemand, Balsa Terzic
Abstract: We use techniques from nonparametric function estimation theory to extract the density profiles, and their derivatives, from a set of N-body dark matter halos. We consider halos generated from ΛCDM simulations of gravitational clustering, as well as isolated, spherical collapses. The logarithmic density slopes γ = d(log ρ)/d(log r) of the ΛCDM halos are found to vary as power-laws in radius, reaching values of γ around -1 at the innermost resolved radii (~0.01 rvirial). This behavior is significantly different from that of broken power-law models like the NFW profile, but similar to that of models like de Vaucouleurs'. Accordingly, we compare the N-body density profiles with various parametric models to find which provide the best fit. We consider an NFW-like model with arbitrary inner slope; Dehnen & McLaughlin's anisotropic model; Einasto's model (identical in functional form to Sersic's model but fit to the space density); and the density model of Prugniel & Simien that was designed to match the deprojected form of Sersic's R1/n law. Overall, the best-fitting model to the ΛCDM halos is Einasto's, although the Prugniel-Simien and Dehnen-McLaughlin models also perform well. With regard to the spherical collapse halos, both the Prugniel-Simien and Einasto models describe the density profiles well, with an rms scatter some four times smaller than that obtained with either the NFW-like model or the 3-parameter Dehnen-McLaughlin model. Finally, we confirm recent claims of a systematic variation in profile shape with halo mass.