Disentangling the Virgo Overdensity with RR Lyrae stars
  We use a combination of spatial distribution and radial velocity to search
for halo sub-structures in a sample of 412 RR Lyrae stars (RRLS) that covers a
$\sim 525$ square degrees region of the Virgo Overdensity (VOD) and spans
distances from the Sun from 4 to 75 kpc. With a friends-of-friends algorithm we
identified six high significance groups of RRLS in phase space, which we
associate mainly with the VOD and with the Sagittarius stream. Four other
groups were also flagged as less significant overdensities. Three high
significance and 3 lower significance groups have distances between $\sim 10$
and 20 kpc, which places them with the distance range attributed by others to
the VOD. The largest of these is the Virgo Stellar Stream (VSS) at 19 kpc,
which has 18 RRLS, a factor of 2 increase over the number known previously.
While these VOD groups are distinct according to our selection cirteria, their
overlap in position and distance, and, in a few cases, similarity in radial
velocity are suggestive that they may not all stem separate accretion events.
Even so, the VOD appears to be caused by more than one overdensity. The Sgr
stream is a very obvious feature in the background of the VOD at a mean
distance of 44 kpc. Two additional high significant groups were detected at
distances $>40$ kpc. Their radial velocities and locations differ from the
expected path of the Sgr debris in this part of the sky, and they are likely to
be remnants of other accretion events.
