The influence of filtering the power spectrum and adding thermal energy on the structure of dark matter halos

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  • 27 October 2000
Abstract
We explore the density profiles of dark matter halos formed in high-resolution cosmological N-body simulations with power spectra damped below a given length scale R_f. The density profile shape of halos with masses smaller than the mass M_f corresponding to R_f does not significantly differ from that of the cold dark matter (CDM) halos; on the average, this shape is well described by the NFW profile but with concentrations lower than in the CDM case: while for the former halos the concentration remains constant with decreasing the mass, for the latter ones it continues increasing. The cosmogony of the former halos is not hierarchical but due to fragmentation of pancakes, their typical formation epoch being slightly later than that of halos of mass close to M_f. The lower concentrations of these halos relative to the CDM ones may be explained by their late formation. If the suppression of power is associated with the free-streaming damping characteristic for warm dark matter (WDM) particles, then particles will have a residual thermal velocity dispersion v_t. We have included this velocity dispersion in our simulations and have found that its influence on the halo structure is negligible. Using an analytical formalism, we show that halos formed by monolithic collapse will present a significant soft core only when particles have velocity dispersions much larger than the v_t of warm particles. Relative to CDM, in a WDM model with R_f=0.15-0.20 Mpc (flat cosmology with \Omega_\Lambda=h=0.7) we find that not only the number of satellite galaxies in Milky-Way systems is in better agreement with the observations, but also the concentrations, the Tully-Fisher relation, and the formation epochs of dwarf galaxies.

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