They Might Be Giants: An Efficient Color-Based Selection of Red Giant
  Stars
  We present a color-based method for identifying red giants based on
Pan-STARRS grz and WISE W1 and W2 photometry. We utilize a subsample of bright
stars with precise parallaxes from Gaia DR2 to verify that the color-based
selection reliably separates dwarfs from giants. The selection is conservative
in the sense that contamination is small (~30%) but not all giants are included
(the selection primarily identifies K giants). The color-based selection can be
applied to stars brighter than $W1\approx16$, more than two magnitudes fainter
than techniques relying on shallower 2MASS photometry. Many streams and clouds
are visible in the resulting sky maps, especially when binned by Gaia DR2
proper motions, including the Sagittarius stream, the Hercules-Aquila Cloud,
the Eastern Banded Structure, Monoceros, and the Virgo Overdensity. In addition
to the characterization of new and known stellar streams, we expect that this
method for selecting red giants will enable detailed analysis of the diffuse
stellar halo to distances exceeding 100 kpc.
