The number and size of subhalo-induced gaps in stellar streams
  Ample observational capabilities exist today to detect the small density
perturbations that low-mass dark matter subhaloes impart on stellar streams
from disrupting Galactic satellites. In anticipation of these observations, we
investigate the expected number and size of gaps by combining an analytic
prescription for gap evolution on circular orbits with the flux of subhaloes
near the stream. We explore the distribution of gap sizes and depths for a
typical cold stream around the Milky Way and find that for a given stream age
and gap depth, each subhalo mass produces a characteristic gap size. For a
stream with an age of a few Gyr, orbiting at a distance of 10-20 kpc from the
Galactic center, even modest subhaloes with a mass of $10^6-10^7 M_\odot$
produce gaps with sizes that are on the order of several degrees. We consider
the number and distribution of gap sizes created by subhaloes with masses
$10^5-10^9 M_\odot$, accounting for the expected depletion of subhaloes by the
Milky Way disk, and present predictions for six cold streams around the Milky
Way. For Pal 5, we forecast 0.7 gaps with a density depletion of at least 25\%
and a typical gap size of $8^\circ$. Thus, there appears to be {\it no tension}
between the recent non-detection of density depletions in the Pal 5 tidal tails
and $\Lambda$CDM expectations. These predictions can be used to guide the scale
of future gap searches.
