Cusps and Cores in galaxies, problems and solutions

Antonino del Popolo

Abstract
Despite the fact that the CDM model is often referred to as "concordance model",
to emphasize that its predictions are in agreement with current observations,
some discrepancy with observations has emerged on scales from a few kpc to tens
of pc. Examples of the quoted tension are: the missing satellite problem, the
angular momentum catastrophe, the too big to fail problem, and the cusp/core
problem.

While numerical simulations universally produce a cuspy density profile,
observed rotation curves of dwarf spiral and low surface brightness (LSB)
galaxies, and clusters of galaxies center give strong indication that the shape
of the density profile at small scales is significantly shallower than profiles
found in numerical simulations. The quoted discrepancy between simulations and
observations has become known as the Cusp/Core problem.

In these lectures, I review the problem and discuss some solutions.

In the first lecture I describe the characteristics of the density profiles
obtained in dissipationless N-body simulations, and the density profiles
observed in galaxies and clusters, together with the methods used to obtain
them.

In the second I discuss the solutions proposed, and in the third I discuss the
role of supernovae feedback, and that of the interaction of baryonic clumps
with dark matter, though dynamical friction, in the solution of the problem.


In particular, I discuss how a secondary infall model, taking into account the
effect of ordered and random angular momentum, dynamical friction, and baryons
adiabatic contraction, can produce profiles in agreement with observations.