The Density Profiles of the Dark Matter Halo Are Not Universal

We perform a series of high-resolution N-body simulations designed to examine the density profiles of dark matter halos. From 12 simulated halos ranging in mass from 2×10¹² to 5×10¹⁴ h^-1 M_solar (represented by ~1 million particles within the virial radius), we find a clear systematic correlation between the halo mass and the slope of the density profile at 1% of the virial radius, in addition to the variations of the slope among halos of similar mass. More specifically, the slope is ~-1.5, -1.3, and -1.1 for galaxy-, group-, and cluster-mass halos, respectively. While we confirm the earlier simulation results that the inner slope is steeper than the universal profile originally proposed by Navarro, Frenk, & White, this mass dependence is inconsistent with several analytical arguments attempting to link the inner slope with the primordial index of the fluctuation spectrum. Thus, we conclude that the dark matter density profiles, especially in the inner region, are not universal.