An extended view of the Pisces Overdensity from the SCUSS survey
  SCUSS is a u-band photometric survey covering about 4000 square degree of the
South Galactic Cap, reaching depths of up to 23 mag. By extending around 1.5
mag deeper than SDSS single-epoch u data, SCUSS is able to probe much a larger
volume of the outer halo, i.e. with SCUSS data blue horizontal branch (BHB)
stars can trace the outer halo of the Milky Way as far as 100-150 kpc.
Utilizing this advantage we combine SCUSS u band with SDSS DR9 gri photometric
bands to identify BHB stars and explore halo substructures. We confirm the
existence of the Pisces overdensity, which is a structure in the outer halo (at
around 80 kpc) that was discovered using RR Lyrae stars. For the first time we
are able to determine its spatial extent, finding that it appears to be part of
a stream with a clear distance gradient. The stream, which is ~5 degrees wide
and stretches along ~25 degrees, consists of 20-30 BHBs with a total
significance of around 6sigma over the background. Assuming we have detected
the entire stream and that the progenitor has fully disrupted, then the number
of BHBs suggests the original system was similar to smaller classical or a
larger ultra-faint dwarf galaxy. On the other hand, if the progenitor still
exists, it can be hunted for by reconstructing its orbit from the distance
gradient of the stream. This new picture of the Pisces overdensity sheds new
light on the origin of this intriguing system.
