出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：High resolution N-body simulations have all but converged on a common empirical form for the
shape of the density profiles of halos, but the full understanding of the underlying physics of halo
formation has eluded them so far. We investigate the formation and structure of dark matter halos
using analytical and semi-analytical techniques. Our halos are formed via an extended secondary
infall model (ESIM); they contain secondary perturbations and hence random tangential and radial
motions which affect the halo’s evolution at it undergoes shell-crossing and virialization.
Even though the density profiles of NFW and ESIM halos are different their phase-space density
distributions are the same: r s3 µ r
a, with a
1
875 over
3 decades in radius. We use two
approaches to try to explain this “universal” slope: (1) The Jeans equation analysis yields many
insights, however, does not answer why a
1
875. (2) The secondary infall model of the 1960’s
and 1970’s, augmented by “thermal motions” of particles does predict that halos should have
a
1
875. However, this relies on assumptions of spherical symmetry and slow accretion. While
for ESIM halos these assumptions are justified, they most certainly break down for simulated
halos which forms hierarchically. We speculate that our argument may apply to an “on-average”
formation scenario of halos within merger-driven numerical simulations, and thereby explain why
a
1
875 for NFW halos. Thus, r s3 µ r
1
875 may be a generic feature of violent relaxation.
