Group Finding in the Stellar Halo using Photometric Surveys: Current
  Sensitivity and Future Prospects
  The ubiquity of substructure in the stellar halo has already been
demonstrated by the SDSS and 2MASS and future surveys promise to explore the
halo in ever more detail. This paper examines what can be learnt from current
and future photometric-databases using group-finding techniques. We compare
groups recovered from a sample of M-giants from 2MASS with those found in
synthetic surveys of simulated $\Lambda$CDM stellar halos and demonstrate broad
consistency. We also find that these recovered groups are likely to represent
the majority of high-luminosity ($\log(L/L_{Sun})>6.67$) satellites accreted
within the last 10 Gyr and on orbits with apocenters within 100 kpc. However
the sensitivity of the M-giant survey to accretion events that were either
ancient, from low-luminosity objects or those on radial orbits is limited
because of the low number of stars, bias towards high-metallicity stars and the
shallow depth. We examine the extent to which these limitations are addressed
by current and future surveys, in particular catalogues of main-sequence
turn-off (MSTO) stars from SDSS and LSST, and of RR-Lyrae stars from LSST or
PanSTARRS. The MSTO surveys are more sensitive to low-luminosity events
($\log(L/L_{Sun}~5$ or less) than the 2MASS M-giant sample, while the RR-Lyrae
surveys, with superior depth, are good at detecting events on highly eccentric
orbits. When combined we expect these photometric surveys to provide a
comprehensive picture of the last 10 Gyr of Galactic accretion. Events older
than this are too phase mixed to be discovered and would require additional
information such as velocity and chemical abundance.
