THE CUSP/CORE PROBLEM AND THE SECONDARY INFALL MODEL

Abstract

We study the cusp/core problem using a secondary infall model (SIM) that takes into account the effect of ordered and random angular momentum, dynamical friction and baryons adiabatic contraction. The model is applied to structures on galactic scales (normal and dwarfs spiral galaxies) and on clusters of galaxies scales. Our analysis suggest that angular momentum and dynamical friction are able, on galactic scales, to overcome the competing effect of adiabatic contraction eliminating the cusp. The slope of density profile of inner haloes flattens with decreasing halo mass and the profile is well approximated by a Burkert's profile. In order to obtain the NFW profile, starting from the profiles obtained from our model, the magnitude of angular momentum and dynamical friction must be reduced with respect to the values predicted by the model itself. The rotation curves of four LSB galaxies from Gentile et al. (2004) are compared to the rotation curves obtained by the model in the present paper obtaining a good fit to the observational data. The time evolution of the density profile of a galaxy of $10^8-10^9 M_{\odot}$ shows that after a transient steepening, due to the adiabatic contraction, the density profile flattens to $\alpha \simeq 0$. On cluster scales we observe a similar evolution of the dark matter density profile but in this case the density profile slope flattens to $\alpha \simeq 0.6$ for a cluster of $\simeq 10^{14} M_{\odot}$. The total mass profile, differently from that of dark matter, shows a central cusp well fitted by a NFW model.