The power spectrum dependence of dark matter halo concentrations

High-resolution N-body simulations are used to examine the power spectrum d ependence of the concentration of galaxy-sized dark matter halos. It is fou nd that dark halo concentrations depend on the amplitude of mass fluctuatio ns as well as on the ratio of power between small and virial mass scales. T his finding is consistent with the original results of Navarro, Frenk, and White (NFW) and allows their model to be extended to include power spectra substantially different from cold dark matter (CDM). In particular, the sin gle-parameter model presented here fits the concentration dependence on hal o mass for truncated power spectra, such as those expected in the warm dark matter scenario, and predicts a stronger redshift dependence for the conce ntration of CDM halos than proposed by NFW. The latter conclusion confirms recent suggestions by Bullock and coworkers, although this new modeling dif fers from theirs in detail. These findings imply that observational limits on the concentration, such as those provided by estimates of the dark matte r content within individual galaxies, may be used to constrain the amplitud e of mass fluctuations on galactic and subgalactic scales. The constraints on Lambda CDM models posed by the dark mass within the solar circle in the Milky Way and by the zero point of the Tully-Fisher relation are revisited, with the result that neither data set is clearly incompatible with the "co ncordance" (Omega (o) = 0.3, Lambda (o) = 0.7, sigma (8) = 0.9) Lambda CDM cosmogony. This conclusion differs from that reached recently by Navarro an d Steinmetz, a disagreement that can be traced to inconsistencies in the no rmalization of the Lambda CDM power spectrum used in that work.