Before the Bar: Kinematic Detection of A Spheroidal Metal-Poor Bulge Component

Abstract

We present 947 radial velocities of RR Lyrae variable stars in four fields located toward the Galactic bulge, observed within the data from the ongoing Bulge RR Lyrae Radial Velocity Assay (BRAVA-RR). We show that these RR Lyrae stars exhibit hot kinematics and null or negligible rotation and are therefore members of a separate population from the bar/pseudobulge that currently dominates the mass and luminosity of the inner Galaxy. Our RR Lyrae stars predate these structures, and have metallicities, kinematics, and spatial distribution that are consistent with a "classical" bulge, although we cannot yet completely rule out the possibility that they are the metal-poor tail of a more metal rich ([Fe/H] ~ -1 dex) halo-bulge population. The complete catalog of radial velocities for the BRAVA-RR stars is also published electronically.

accepted to ApJL

References in corpus (8)

• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way
• Metal-poor stars towards the Galactic bulge - a population potpourri
• Why the Milky Way's bulge is not only a bar formed from a cold thin disk
• The Argo Simulation: II. The Early Build-up of the Hubble Sequence
• An Observational Guide to Identifying Pseudobulges and Classical Bulges in Disk Galaxies
• The Anisotropic Spatial Distribution of Hypervelocity Stars
• Metallicity Bias in the Kinematics of the Milky Way Stellar Halo

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