Suppressing Linear Power on Dwarf Galaxy Halo Scales

Recently is has been suggested that the dearth of small halos around the Milky Way arises due to a modification of the primordial power spectrum of fluctuations from inflation. Such modifications would be expected to alter the formation of structure from bottom-up to top-down on scales near where the short-scale power has been suppressed. Using cosmological simulations we study the effects of such a modification of the initial power spectrum. While the halo multiplicity function depends primarily on the linear theory power spectrum, most other probes of power are more sensitive to the non-linear power spectrum. Collapse of large-scale structures as they go non-linear regenerates a “tail” in the power spectrum, masking small-scale modifications to the primordial power spectrum except at very high-z. Even the small-scale (k > 2 h Mpc) clustering of the Ly-α forest is affected by this process, so that CDM models with sufficient power suppression to reduce the number of 10M⊙ halos by a factor of ∼ 5 give similar Ly-α forest power spectrum results. We conclude that other observations that depend more directly on the number density of collapsed objects, such as the number of damped Ly-α systems, or the redshift of reionization may provide the most sensitive tests of these models. Subject headings: cosmology:theory – large-scale structure of universe