The Pal 5 Star Stream Gaps
  Pal 5 is a low mass, low velocity dispersion, globular cluster with
spectacular tidal tails. We use the SDSS DR8 data to extend the density
measurements of the trailing star stream to 23 degrees distance from the
cluster, at which point the stream runs off the edge of the available sky
coverage. The size and the number of gaps in the stream are measured using a
filter which approximates the structure of the gaps found in stream
simulations. We find 5 gaps that are at least 99% confidence detections with
about a dozen gaps at 90% confidence. The statistical significance of a gap is
estimated using bootstrap re-sampling of the control regions on either side of
the stream. The density minimum closest to the cluster is likely the result of
the epicyclic orbits of the tidal outflow and has been discounted. To create
the number of 99% confidence gaps per unit length at the mean age of the stream
requires a halo population of nearly a thousand dark matter sub-halos with peak
circular velocities above 1 km/s within 30kpc of the galactic center. These
numbers are a factor of about 3 below cold stream simulation at this sub-halo
mass or velocity, but given the uncertainties in both measurement and more
realistic warm stream modeling, are in substantial agreement with the LCDM
prediction
