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We report the discovery of two new halo velocity groups (Cancer groups A andB) traced by 8 distant RR Lyrae stars and observed by the Palomar TransientFactory (PTF) survey at R.A.~129 deg, Dec~20 deg (l~205 deg, b~32 deg). Locatedat 92 kpc from the Galactic center (86 kpc from the Sun), these are some of themost distant substructures in the Galactic halo known to date. Follow-upspectroscopic observations with the Palomar Observatory 5.1-m Hale telescopeand W. M. Keck Observatory 10-m Keck I telescope indicate that the two groupsare 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 velocitydispersions of \sigma_{v_{gsr}}=12.4+-5.0 km/s and \sigma_{v_{gsr}}=14.9+-6.2km/s, and are spatially extended (about several kpc) making it very unlikelythat they are bound systems, and are more likely to be debris of tidallydisrupted 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 asomewhat uncertain (due to small sample size) metallicity dispersion of ~0.4dex, suggesting dwarf galaxies as progenitors. Two additional RR Lyrae starswith velocities consistent with those of the Cancer groups have been observed~25 deg east, suggesting possible extension of the groups in that direction.

Two Distant Halo Velocity Groups Discovered by the Palomar Transient Factory