Predictably Missing Satellites: Subhalo Abundance in Milky Way-like
  Halos
  On small scales there have been a number of claims of discrepancies between
the standard Cold Dark Matter (CDM) model and observations. The 'missing
satellites problem' infamously describes the overabundance of subhalos from CDM
simulations compared to the number of satellites observed in the Milky Way. A
variety of solutions to this discrepancy have been proposed; however, the
impact of the specific properties of the Milky Way halo relative to the typical
halo of its mass have yet to be explored. Motivated by recent studies that
identified ways in which the Milky Way is atypical (e.g., Licquia et al. 2015),
we investigate how the properties of dark matter halos with mass comparable to
our Galaxy's --- including concentration, spin, shape, and scale factor of the
last major merger --- correlate with the subhalo abundance. Using zoom-in
simulations of Milky Way-like halos, we build two models of subhalo abundance
as functions of host halo properties and conclude that the Milky Way should be
expected to have 22%-44% fewer subhalos with low maximum rotation velocities
($V_{\rm max}^{\rm sat} \sim 10$kms$^{-1}$) at the 95% confidence level and up
to 72% fewer than average subhalos with high rotation velocities ($V_{\rm
max}^{\rm sat} \gtrsim 30$kms$^{-1}$, comparable to the Magellanic Clouds) than
would be expected for a typical halo of the Milky Way's mass. Concentration is
the most informative single parameter for predicting subhalo abundance. Our
results imply that models tuned to explain the missing satellites problem
assuming typical subhalo abundances for our Galaxy will be over-correcting.
