Using gaps in N-body tidal streams to probe missing satellites
  We use N-body simulations to model the tidal disruption of a star cluster in
a Milky-Way-sized dark matter halo, which results in a narrow stream comparable
to (but slightly wider than) Pal-5 or GD-1. The mean Galactic dark matter halo
is modeled by a spherical Navarro-Frenk-White (NFW) potential with subhalos
predicted by the LCDM cosmological model. The distribution and mass function of
the subhalos follow the results from the Aquarius simulation. We use a matched
filter approach to look for "gaps" in tidal streams at 12 length scales from
0.1 kpc to 5 kpc, which appear as characteristic dips in the linear densities
along the streams. We find that, in addition to the subhalos' perturbations,
the epicyclic overdensities (EOs) due to the coherent epicyclic motions of
particles in a stream also produce gap-like signals near the progenitor. We
measure the gap spectra - the gap formation rates as functions of gap length -
due to both subhalo perturbations and EOs, which have not been accounted for
together by previous studies. Finally, we project the simulated streams onto
the sky to investigate issues when interpreting gap spectra in observations. In
particular, we find that gap spectra from low signal-to-noise observations can
be biased by the orbital phase of the stream. This indicates that the study of
stream gaps will benefit greatly from high-quality data from future missions.
