arXive: 14 October 2010

Dark Matter Halos: The Dynamical Basis of Effective Empirical Models

Authors: A. Lapi (1,2), A. Cavaliere (1) (1-Univ. "Tor Vergata", Roma, Italy, 2-SISSA/ISAS, Trieste, Italy)

http://arxiv.org/abs/1010.2602v1

We investigate the dynamical basis of the classic empirical models (specifically, Sersic-Einasto and generalized NFW) that are widely used to describe the distributions of collisionless matter in galaxies. We submit that such a basis is provided by our \alpha-profiles, shown to constitute solutions of the Jeans dynamical equilibrium with physical boundary conditions. We show how to set the parameters of the empirical in terms of the dynamical models; we find the empirical models, and specifically Sersic-Einasto, to constitute a simple and close approximation to the dynamical models. Finally, we discuss how these provide an useful baseline for assessing the impact of the small-scale dynamics that may modulate the density slope in the central galaxy regions.

 

The Origin of Dark Matter Halo Profiles

Authors: Neal Dalal, Yoram Lithwick, Michael Kuhlen

http://arxiv.org/abs/1010.2539v1

A  longstanding puzzle of fundamental importance in modern cosmology has been the origin of the nearly universal density profiles of dark matter halos found in N-body simulations -- the so-called NFW profile. We show how this behavior may be understood, simply, by applying adiabatic contraction to peaks of Gaussian random fields. We argue that dynamical friction acts to reduce enormously the effect of random scatter in the properties of initial peaks, providing a key simplification. We compare our model predictions with results of the ultra-high resolution Via Lactea-II N-body simulation, and find superb agreement. We show how our model may be used to predict the distribution of halo properties like concentration. Our results suggest that many of the basic properties of halo structure may be understood using extremely simple physics.

 

Particle cosmology

Authors: A. Riotto (CERN)

http://arxiv.org/abs/1010.2642v1

In these lectures the present status of the so-called standard cosmological model, based on the hot Big Bang theory and the inflationary paradigm is reviewed. Special emphasis is given to the origin of the cosmological perturbations we see today under the form of the cosmic microwave background anisotropies and the large scale structure and to the dark matter and dark energy puzzles.