Discovery of a new, polar-orbiting debris stream in the milky way stellar halo

Abstract

We show that there is a low-metallicity tidal stream that runs along l = 143° in the South Galactic Cap, about 34kpc from the Sun, discovered from the Sloan Extension for Galactic Understanding and Exploration stellar velocities. Since the most concentrated detections are in the Cetus constellation, and the orbital path is nearly polar, we name it the Cetus Polar Stream (CPS). Although it is spatially coincident with the Sgr dwarf trailing tidal tail at b = -70°, the metallicities ([Fe/H] = -2.1), ratio of blue straggler to blue horizontal branch stars, and velocities of the CPS stars differ from Sgr. Some CPS stars may contaminate previous samples of Sgr dwarf tidal debris. The unusual globular cluster NGC5824 is located along an orbit fitted to the CPS, with the correct radial velocity. © 2009. The American Astronomical Society.