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

TL;DR

This study analyzes the kinematics of RR Lyrae stars in the Galactic bulge, revealing a distinct, non-rotating, metal-poor population consistent with a classical bulge component, separate from the bar and pseudobulge.

Contribution

The paper provides the first large kinematic dataset of RR Lyrae stars in the bulge, demonstrating their distinct properties and supporting the existence of a classical bulge component.

Findings

RR Lyrae stars show hot kinematics with negligible rotation.

They are likely part of a classical bulge, not the bar or pseudobulge.

The dataset includes 947 radial velocities of RR Lyrae stars.

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.