It is generally believed that the first objects, as well as their subsequent clusterings, have their origin in small amplitude density inhomogeneities which have grown by gravitational instability as the universe expanded. The evolution of density inhomogeneities passes through two distinct stages:
This correlation, as well as other two recently found relating the concentration to the halo formation epoch and the mass inside the scale radius, can be explained through a model of evolution for r_s taking into account that halos grow inside-out (keeping their inner structure unaltered) between major mergers. Here we provide a FORTRAN code that computes the typical r_s value for relaxed halos in CDM cosmologies according to our evolutive model.
Convergence studies in cosmological N-body simulations suggest that
the inner slope of the halo density profile does not tend to a
power-law for vanishing radii, but becomes increasingly
shallower. Thus, NFW-like laws do not fit well the density profile in
the halo inner region. A law with a decreasing inner slope (as the
Sersic law) do a better job in wide range fittings. We have developed
a FORTRAN code that computes
time-independent relations involving scale parameters of the NFW and
Sersic laws. These time-independent relations arise from the
inside-out growth of halos and allows the determination of the profile
parameters for halos of mass M at any time.
We have build an analytic model for a preheated, polytropic hot gas in
hydrostatic equilibrium within an NFW dark halo potential taking into
account the inside-out growth of the halo between major mergers. We
have applied the model to study the observed X-ray properties of
galaxy groups and clusters at z=0.