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 eight distant RR Lyrae stars and observed by the Palomar Transient Factory survey at R. A. similar to 129 degrees, decl. similar to 20 degrees (l similar to 205 degrees, b similar to 32 degrees). 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) over bar (A)(gsr) = 78.0 +/- 5.6 km s(-1) (Cancer group A) and (v) over bar (B)(gsr) = 16.3 +/- 7.1 km s(-1) (Cancer group B). The groups have velocity dispersions of sigma(A)(vgsr) = 12.4 +/- 5.0 km s(-1) and sigma(B)(vgsr) = 14.9 +/- 6.2 km s(-1) and are spatially extended (about several kpc), making it very unlikely that they are bound systems, and more likely to be debris of tidally disrupted dwarf galaxies or globular clusters. Both groups are metal-poor (median metallicities of [Fe/H](A) = -1.6 dex and [Fe/H](B) = -2.1 dex) and have a somewhat uncertain (due to small sample size) metallicity dispersion of similar to 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 similar to 25 degrees east, suggesting possible extension of the groups in that direction.