The Next Generation Virgo Cluster Survey. XIX. Tomography of Milky Way
  Substructures in the NGVS Footprint
  The Next Generation Virgo Cluster Survey (NGVS) is a deep $u^*giz$ survey
targeting the Virgo cluster of galaxies at 16.5~Mpc. This survey provides
high-quality photometry over an $\sim$ 100 deg$^2$ region straddling the
constellations of Virgo and Coma Berenices. This sightline through the Milky
Way is noteworthy in that it intersects two of the most prominent substructures
in the Galactic halo: the Virgo Over-Density (VOD) and Sagittarius stellar
stream (close to its bifurcation point). In this paper, we use deep $u^*gi$
imaging from the NGVS to perform tomography of the VOD and Sagittarius stream
using main-sequence turnoff (MSTO) stars as a halo tracer population. The VOD,
whose centroid is known to lie at somewhat lower declinations ($\alpha \sim
190^\circ$, $\delta \sim -5^\circ$) than is covered by the NGVS, is
nevertheless clearly detected in the NGVS footprint at distances between $\sim$
8 and 25~kpc. By contrast, the Sagittarius stream is found to slice directly
across the NGVS field at distances between 25 and 40~kpc, with a density
maximum at $\simeq$~35~kpc. No evidence is found for new substructures beyond
the Sagittarius stream, at least out to a distance of $\sim$~90 kpc --- the
largest distance to which we can reliably trace the halo using MSTO stars. We
find clear evidence for a distance gradient in the Sagittarius stream across
the $\sim 30$~deg of sky covered by the NGVS and its flanking fields. We
compare our distance measurements along the stream to those predicted by
leading stream models.
