New views of the distant stellar halo
  Currently only a small number of Milky Way (MW) stars are known to exist
beyond 100 kpc from the Galactic center. Though the distribution of these stars
in the outer halo is believed to be sparse, they can provide evidence of more
recent accretion events than in the inner halo and help map out the MW's dark
matter halo to its virial radius. We have re-examined the outermost regions of
11 existing stellar halo models with two synthetic surveys: one mimicking
present-day searches for distant M giants and another mimicking RR Lyrae (RRLe)
projections for LSST. Our models suggest that color and proper motion cuts
currently used to select M giant candidates for follow-up successfully remove
nearly all halo dwarf self-contamination and are useful for focusing
observations on distant M giants, of which there are thousands to tens of
thousands beyond 100 kpc in our models. We likewise expect that LSST will
identify comparable numbers of RRLe at these distances. We demonstrate that
several observable properties of both tracers, such as proximity of neighboring
stars, proper motions, and distances (for RRLe) could help us separate
different accreted structures from one another. We also discuss prospects for
using ratios of M giants to RRLe as a proxy for accretion time, which in the
future could provide new constraints on the recent accretion history of our
Galaxy.
