Kinematics of Tidal Debris from Omega Centauri's Progenitor Galaxy

Abstract

We present the kinematic properties of a tidally disrupted dwarf galaxy in the Milky Way, based on the hypothesis that its central part once contained the most massive Galactic globular cluster, omega Cen. Dynamical evolution of a self-gravitating progenitor galaxy that follows the present-day and likely past orbits of omega Cen is calculated numerically and the kinematic nature of their tidal debris is analyzed, combined with randomly generated stars comprising spheroidal halo and flat disk components. We show that the retrograde rotation of the debris stars at $\sim -100$ km/s accords with a recently discovered, large radial velocity stream at $\sim 300$ km/s towards the Galactic longitude of $\sim 270^\circ$. These stars also contribute, only in part, to a reported retrograde motion of the outer halo at the North Galactic Pole. The prospects for future debris searches and the implications for the early evolution of the Galaxy are briefly presented.Comment: 14 pages, 3 figures, accepted for publication in ApJ Letter