Two Distant Halo Velocity Groups Discovered by the Palomar Transient
  Factory
  We report the discovery of two new halo velocity groups (Cancer groups A and
B) traced by 8 distant RR Lyrae stars and observed by the Palomar Transient
Factory (PTF) survey at R.A.~129 deg, Dec~20 deg (l~205 deg, b~32 deg). Located
at 92 kpc from the Galactic center (86 kpc from the Sun), these are some of the
most distant substructures in the Galactic halo known to date. Follow-up
spectroscopic observations with the Palomar Observatory 5.1-m Hale telescope
and W. M. Keck Observatory 10-m Keck I telescope indicate that the two groups
are moving away from the Galaxy at v_{gsr} = 78.0+-5.6 km/s (Cancer group A)
and v_{gsr} = 16.3+-7.1 km/s (Cancer group B). The groups have velocity
dispersions of \sigma_{v_{gsr}}=12.4+-5.0 km/s and \sigma_{v_{gsr}}=14.9+-6.2
km/s, and are spatially extended (about several kpc) making it very unlikely
that they are bound systems, and are more likely to be debris of tidally
disrupted dwarf galaxies or globular clusters. Both groups are metal-poor
(median metallicities of [Fe/H] = -1.6 dex and [Fe/H] =-2.1 dex), and have a
somewhat uncertain (due to small sample size) metallicity dispersion of ~0.4
dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae stars
with velocities consistent with those of the Cancer groups have been observed
~25 deg east, suggesting possible extension of the groups in that direction.
