Formation and Structure of Halos in a Warm Dark Matter Cosmology

(Abridged) Using high-resolution cosmological N-body simulations, we studyhow the density profiles of dark matter halos are affected by the filtering ofthe density power spectrum below a given scale length and by the introductionof a thermal velocity dispersion. In the warm dark matter (WDM) scenario, boththe free-streaming scale, R_f, and the velocity dispersion, v_w, are determinedby the mass m_w of the WDM particle. We find that v_w is too small to affectthe density profiles of WDM halos. Down to the resolution attained in oursimulations, there is not any significant difference in the density profilesand concentrations of halos obtained in simulations with and without theinclusion of v_w. The density profiles of halos with masses down to ~0.01 thefiltering mass M_f can be described by the NFW shape; significant soft coresare not formed. Nevertheless, the concentrations of these halos are lower thanthose of the CDM counterparts and are approximately independent of mass. Thelower concentrations of WDM halos with respect to their CDM counterparts can beaccounted for their late formation epoch. Overall, our results point to aseries of advantages of a WDM model over the CDM one. In addition to solvingthe substructure problem, a WDM model with R_f~0.16 Mpc (m_w~0.75 kev; flatcosmology with Omega_L=h=0.7) also predicts concentrations, a Tully-Fisherrelation, and formation epochs for small halos which seems to be in betteragreement with observations, relative to CDM predictions.Comment: Accepted for publication in ApJ. 34 pages, figs. 1a,1b, and 1c given in separate files (high resolution versions available at ftp://ftp.astroscu.unam.mx/pub/temporal/). Major modifications after referees Report (more simulations and new figures are presented), but main conclusions remain the sam