Density profiles of dark matter halos in an improved secondary infall model

In this paper we calculate the density profiles of virialized halos both in the case of structure evolving hierarchically from a scale-free Gaussian d elta-field having a power spectrum P(k) proportional to k(n) in a Omega = 1 Universe and in the case of the CDM model, by using a modified version of Hoffman & Shaham's (1985) (hereafter HS) and Hoffman's (1988) model. We sup pose that the initial density contrast profile around local max ima is give n by the mean peak profile introduced by Bardeen et al. (1986) (hereafter B BKS), and is not just proportional to the two-point correlation function, a s assumed by HS. We show that the density profiles, both for scale-free Uni verses and the CDM model, are not power-laws but have a logarithmic slope t hat increases from the inner halo to its outer parts. Both scale-free, for n greater than or equal to -1, and CDM density profiles are well approximat ed by Navarro et al. (1995, 1996, 1997) profile. The radius a, at which the slope alpha = -2, is a function of the mass of the halo and in the scale-f ree models also of the spectral index n.