Secondary infall and dark matter haloes

We test the secondary infall model (SIM) by direct comparison with the results of N-body simulations. Eight cluster-size and six galactic-size dark matter haloes have been selected at z = 0 and resimulated with high resolution. Based on their density profiles at the initial redshift, we compute their evolution by the SIM, assuming a simple prescription for the angular momentum. A comparison of the density profiles obtained by the SIM and the numerical experiments at z = 5, 1 and 0 shows that, for most of the haloes at most epochs, the SIM reproduces the simulated matter distribution with a typical fractional deviation of less than 40 per cent over more than six orders of magnitudes in the density. It is also found that, within the SIM framework, most of the diversity in the shape of the density profiles at z = 0 arises from the scatter in the primordial spherically averaged density profile rather than the scatter in the angular momentum distribution. A crude optimization shows that a similar degree of agreement is obtained for galactic and cluster haloes, but the former seem to require slightly higher amounts of angular momentum. Our main conclusion is that the SIM provides a viable dynamical model for predicting the structure and evolution of the density profile of dark matter haloes.