EXPLORING HALO SUBSTRUCTURE WITH GIANT STARS: SUBSTRUCTURE IN THE LOCAL HALO AS SEEN IN THE GRID GIANT STAR SURVEY INCLUDING EXTENDED TIDAL DEBRIS FROM ωCENTAURI

• Published in: Astrophysical journal. Letters Vol. 747; no. 2; pp. 1 - 6
• Main Authors: Majewski, Steven R, NIDEVER, DAVID L, Smith, Verne V, Damke, Guillermo J, Kunkel, William E, Patterson, Richard J, Bizyaev, Dmitry, PEREZ, ANA E GARCIA
• Format: Journal Article
• Language: English
• Published: 10.03.2012
• Subjects: Debris; Dwarf galaxies; Giant stars; Halos; Quadrants; Stars; Streams; Substructures
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/747/2/L37

We present the latitude-normalized radial velocity ([upsilon] sub(b)) distribution of 3318 subsolar metallicity, V [<, ~] 13.5 stars from the Grid Giant Star Survey (GGSS) in southern hemisphere fields. The sample includes giants mostly within ~5 kpc from the Galactic disks and halo. The nearby halo is found to (1) exhibit significant kinematical substructure, and (2) be prominently represented by several velocity coherent structures, including a very retrograde "cloud" of stars at l ~ 285[degrees] and extended, retrograde "streams" visible as relatively tight l-[upsilon] sub(b) sequences. One sequence in the fourth Galactic quadrant lies within the l-[upsilon] sub(b) space expected to contain tidal debris from the "star cluster" omega Centauri. Not only does omega Cen lie precisely in this l-[upsilon] sub(b) sequence, but the positions and [upsilon] sub(b) of member stars match those of N-body simulations of tidally disrupting dwarf galaxies on orbits ending with omega Cen's current position and space motion. But the ultimate proof that we have very likely found extended parts of the ?Cen tidal stream comes from echelle spectroscopy of a subsample of the stars that reveals a very particular chemical abundance signature known to occur only in omega Cen. The newly discovered omega Cen debris accounts for almost all fourth Galactic quadrant retrograde stars in the southern GGSS, which suggests omega Cen is a dominant contributor of retrograde giant stars in the inner Galaxy.