The dearth of halo dwarf galaxies: is there power on short scales?

TL;DR

N-body simulations of structure formation with scale-invariant primordial perturbations show significantly more virialized objects of dwarf-galaxy mass in a typical galactic halo than are observed around the Milky Way.

Abstract

N-body simulations of structure formation with scale-invariant primordial perturbations show significantly more virialized objects of dwarf-galaxy mass in a typical galactic halo than are observed around the Milky Way. We show that the dearth of observed dwarf galaxies could be explained by a dramatic downturn in the power spectrum at small distance scales. This suppression of small-scale power might also help mitigate the disagreement between cuspy simulated halos and smooth observed halos, while remaining consistent with Lyman-alpha-forest constraints on small-scale power. Such a spectrum could arise in inflationary models with broken scale invariance.

Figures (2)

• Figure 1: The upper panel shows the power spectrum for $\Gamma=0.25$ CDM (solid curve), for a model in which the power spectrum is arbitrarily cut off at $k=4.5\,h$ Mpc (dotted curve), and the broken-scale-invariance inflation model (dashed curve). The lower panel shows the rms mass fluctuation as a function of the enclosed mean mass $M$ for these three models.
• Figure 2: The cumulative number of mini-halos for the power spectra shown in Fig. \ref{['fig:powerspectrum']} as a function of the circular speed $v_{{\rm c}}$ of the halo divided by the circular speed $v_{\rm global}$ of the Galactic halo. The points show the Milky Way satellites. Compare with Fig. 1 in Ref. Mooetal99.