The structure and dynamical evolution of dark matter haloes

(Shortened) We use N-body simulations to investigate the structure anddynamical evolution of dark matter halos in galaxy clusters. Our sampleconsists of nine massive halos from an EdS universe with scale free powerspectrum and n = -1. Halos are resolved by ~20000 particles each, with adynamical resolution of 20-25 kpc. Large scale tidal fields are included up toL=150 Mpc using background particles. The halo formation process can becharacterized by the alternation of two dynamical configurations: a mergingphase and a relaxation phase, defined by their signature on the evolution ofthe total mass and rms velocity. Halos spend on average one 1/3 of theirevolution in the merging phase and 2/3 in the relaxation phase. Using thisdefinition, we study the density profiles and their change during the halohistory. The average density profiles are fitted by the NFW analytical modelwith an rms residual of 17% between the virial radius Rv and 0.01 Rv. TheHernquist (1990) profiles fits the same halos with an rms residual of 26%. Thetrend with mass of the scale radius of these fits is marginally consistent withthat found by Cole & Lacey (1996): in comparison our halos are more centrallyconcentrated, and the relation between scale radius and halo mass is slightlysteeper. We find a moderately large scatter in this relation, due both todynamical evolution within halos and to fluctuations in the halo population. Weanalyze the dynamical equilibrium of our halos using the Jeans' equation, andfind that on average they are approximately in equilibrium within their virialradius. Finally, we find that the projected mass profiles of our simulatedhalos are in very good agreement with the profiles of three rich galaxyclusters derived from strong and weak gravitational lensing observations.Comment: 20 pages, Latex, with all figures included. Modified to match the published versio