The structure and dynamical evolution of dark matter haloes

Abstract

We use N-body simulations to investigate the structure and dynamical evolution of dark matter halos in clusters of galaxies. Our sample consists of nine massive halos from an Einstein-De Sitter universe with scale free power spectrum and spectral index n = -1. Halos are resolved by 20000 particles each, on average, and have a dynamical resolution of 20-25 kpc, as shown by extensive tests. We find that the halo formation process can be characterized by the alternation of two dynamical configurations: a merging phase and a relaxation phase, defined by their signature on the evolution of the total mass and rms velocity. Using this definition, we study the halo density profiles and show how they change during the halo dynamical history. In particular, we find that the average density profiles of our halos are fitted by the Navarro, Frenk \\& White (1995) analytical model with an \\rms residual of 17\\% between the virial radius R_v and 0.01 R_v. The Hernquist (1990) analytical density profiles fits the same halos with an \\rms residual of 26%. The trend with mass of the scale radius of these fits is marginally consistent with that found by Cole \\& Lacey (1996): compared to their results our halos are more centrally concentrated, and the relation between scale radius and halo mass is slightly steeper. We find a moderately large scatter in this relation, due both to dynamical evolution within halos and to fluctuations in the halo population. We analyze the dynamical equilibrium of our halos using the Jeans' equation, and find that on average they are approximately in equilibrium within their virial radius. Finally, we find that the projected mass profiles of our simulated halos are in very good agreement with the profiles of three rich galaxy clusters derived from strong and weak gravitational lensing observations.

Keywords

Affiliated Institutions

• Institute of Astronomy RU
• Max Planck Society DE
• University of Cambridge GB
• Institut d'Astrophysique de Paris FR

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