Commissioning observations with the Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, have produced radial velocities (RVs) for ~4700 K/M-giant stars in the Milky Way bulge. These high-resolution (R \sim 22,500), high-S/N (>100 per resolution element), near-infrared (1.51-1.70 um; NIR) spectra provide accurate RVs (epsilon_v~0.2 km/s) for the sample of stars in 18 Galactic bulge fields spanning -1<l<20 deg, |b|<20 deg, and dec>-32 deg. This represents the largest NIR high-resolution spectroscopic sample of giant stars ever assembled in this region of the Galaxy. A cold (sigma_v~30 km/s), high-velocity peak (V_GSR \sim +200 km/s) is found to comprise a significant fraction (~10%) of stars in many of these fields. These high RVs have not been detected in previous MW surveys and are not expected for a simple, circularly rotating disk. Preliminary distance estimates rule out an origin from the background Sagittarius tidal stream or a new stream in the MW disk. Comparison to various Galactic models suggests that these high RVs are best explained by stars in orbits of the Galactic bar potential, although some observational features remain unexplained.
@article{arxiv.1207.3797,
title = {The Apache Point Observatory Galactic Evolution Experiment: First Detection of High Velocity Milky Way Bar Stars},
author = {David L. Nidever and Gail Zasowski and Steven R. Majewski and Jonathan Bird and Annie C. Robin and Inma Martinez-Valpuesta and Rachael L. Beaton and Ralph Schoenrich and Mathias Schultheis and John C. Wilson and Michael F. Skrutskie and Robert W. O'Connell and Matthew Shetrone and Ricardo P. Schiavon and Jennifer A. Johnson and Benjamin Weiner and Ortwin Gerhard and Donald P. Schneider and Carlos Allende Prieto and Kris Sellgren and Dmitry Bizyaev and Howard Brewington and Jon Brinkmann and Daniel J. Eisenstein and Peter M. Frinchaboy and Ana Elia Garcia Perez and Jon Holtzman and Fred R. Hearty and Elena Malanushenko and Viktor Malanushenko and Demitri Muna and Daniel Oravetz and Kaike Pan and Audrey Simmons and Stephanie Snedden and Benjamin A. Weaver},
journal= {arXiv preprint arXiv:1207.3797},
year = {2015}
}
Comments
7 pages, 4 figures, accepted for publication in ApJ Letters