The Cusp/Core Problem and the Secondary Infall Model

We study the cusp/core problem using a secondary infall model that takes into account the effect of orderedand random angular momentum, dynamical friction, and baryons adiabatic contraction (AC). The model isapplied 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 overcomethe competing effect of AC eliminating the cusp. The slope of density profile of inner halos flattens withdecreasing halo mass and the profile is well approximated by a Burkert’s profile. In order to obtain theNavarro–Frenk–White (NFW) profile, starting from the profiles obtained from our model, the magnitude ofangular momentum and dynamical friction must be reduced with respect to the values predicted by the modelitself. The rotation curves of four lower sideband galaxies from Gentile et al. are compared to the rotationcurves obtained by the model in the present paper obtaining a good fit to the observational data. The timeevolution of the density profile of a galaxy of 108–109M shows that after a transient steepening, due to theAC, the density profile flattens to α 0. On cluster scales we observe a similar evolution of the dark matter(DM) density profile but in this case the density profile slope flattens to α 0.6 for a cluster of 1014M.The total mass profile, differently from that of DM, shows a central cusp well fitted by an NFW model.