Spectroscopic confirmation of the pisces overdensity

Abstract

We present spectroscopic confirmation of the "Pisces Overdensity," also known as "Structure J," a photometric overdensity of RR Lyrae stars discovered by the Sloan Digital Sky Survey at an estimated photometric distance of 85 kpc. We measure radial velocities for eight RR Lyrae stars within Pisces. We find that five of the eight stars have heliocentric radial velocities within a narrow range of -87 km s-1 < vr < -67 km s-1, suggesting that the photometric overdensity is mainly due to a physically associated system, probably a dwarf galaxy or a disrupted galaxy. Two of the remaining three stars differ from one another by only 9 km s-1, but it would be premature to identify them as a second system. © 2009. The American Astronomical Society. All rights reserved.