Separating the conjoined red clump in the Galactic Bulge: Kinematics and Abundances

Abstract

We have used the AAOMEGA spectrograph to obtain R $\sim 1500$ spectra of 714 stars that are members of two red clumps in the Plaut Window Galactic bulge field $(l,b)=0^{\circ },-8^{\circ }$. We discern no difference between the clump populations based on radial velocities or abundances measured from the Mg$b$ index. The velocity dispersion has a strong trend with Mg$b$-index metallicity, in the sense of a declining velocity dispersion at higher metallicity. We also find a strong trend in mean radial velocity with abundance. Our red clump sample shows distinctly different kinematics for stars with [Fe/H] $<-1$, which may plausibly be attributable to a minority classical bulge or inner halo population. The transition between the two groups is smooth. The chemo-dynamical properties of our sample are reminiscent of those of the Milky Way globular cluster system. If correct, this argues for no bulge/halo dichotomy and a relatively rapid star formation history. Large surveys of the composition and kinematics of the bulge clump and red giant branch are needed to define further these trends.

5 pages, 4 figures, Accepted for Publication in the Astrophysical Journal Letters Fixed typos, updated affiliations and added some references upon request

References in corpus (11)

• Two Red Clumps and the X-Shaped Milky Way Bulge
• Chemical similarities between Galactic bulge and local thick disk red giant stars
• Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
• Modelling the Galactic bar using OGLE-II Red Clump Giant Stars
• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• Kinematics at the Edge of the Galactic Bulge: Evidence for Cylindrical Rotation
• The Bulge Radial Velocity Assay (BRAVA): I. Sample Selection and a Rotation Curve
• Formation & evolution of the Galactic bulge: constraints from stellar abundances
• Proper Motions in the Galactic Bulge: Plaut's Window
• Fabry-Perot Absorption Line Spectroscopy of the Galactic Bar. II. Stellar Metallicities
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. III. Detection of lithium in the metal-poor bulge dwarf MOA-2010-BLG-285S

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