Characterizing the SHARDS of Disrupted Milky Way Satellites with LAMOST
  We derive the fraction of substructure in the Galactic halo using a sample of
over 10,000 spectroscopically-confirmed halo giant stars from the LAMOST
spectroscopic survey. By observing 100 synthetic models along each line of
sight with the LAMOST selection function in that sky area, we statistically
characterize the expected halo populations. We define as SHARDS (Stellar Halo
Accretion Related Debris Structures) any stars in >3-sigma excesses above the
model predictions. We find that at least 10% of the Milky Way halo stars from
LAMOST are part of SHARDS. By running our algorithm on smooth halos observed
with the LAMOST selection function, we show that the LAMOST data contain excess
substructure over all Galactocentric radii R_GC < 40 kpc, beyond what is
expected due to statistical fluctuations and incomplete sampling of a smooth
halo. The level of substructure is consistent with the fraction of stars in
SHARDS in model halos created entirely from accreted satellites. This work
illustrates the potential of vast spectroscopic surveys with high filling
factors over large sky areas to recreate the merging history of the Milky Way.
