Kinematics of RR Lyrae stars in the Galactic bulge with OGLE-IV and Gaia DR2

Abstract

We analyze the kinematics and spatial distribution of 15,599 fundamental-mode RR Lyrae (RRL) stars in the Milky Way bulge by combining OGLE-IV photometric data and Gaia DR2 proper motions. We show that the longitudinal proper motions and the line-of-sight velocities can give similar results for the rotation in the Galactic central regions. The angular velocity of bulge RRLs is found to be around $35$ km s${}^{-1}$ kpc${}^{-1}$, significantly smaller than that for the majority of bulge stars ($50-60$ km s${}^{-1}$ kpc${}^{-1}$); bulge RRLs have larger velocity dispersion (120$-$140 km s${}^{-1}$) than younger stars. The dependence of the kinematics of the bulge RRLs on their metallicities is shown by their rotation curves and spatial distributions. Metal-poor RRLs ([Fe/H]<$-1$) show a smaller bar angle than metal-rich ones. We also find clues suggesting that RRLs in the bulge are not dominated by halo stars. These results might explain some previous conflicting results over bulge RRLs and help understand the chemodynamical evolution of the Galactic bulge.

15 pages, 15 figures. Published by MNRAS

References in corpus (20)

• The Gaia mission
• 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 GIRAFFE Inner Bulge Survey (GIBS) III. Metallicity distributions and kinematics of 26 Galactic bulge fields
• The Gaia-ESO Survey: metallicity and kinematic trends in the Milky Way bulge
• ARGOS II: The Galactic Bulge Survey
• The Bulge Radial Velocity Assay (BRAVA): I. Sample Selection and a Rotation Curve
• The Pristine Inner Galaxy Survey (PIGS) I: Tracing the kinematics of metal-poor stars in the Galactic bulge
• Fourier Dissection of Early-Type Galaxy Bars
• A parametric description of the 3D structure of the Galactic Bar/Bulge using the VVV survey
• Variable stars in the VVV globular clusters. I. 2MASS-GC02 and Terzan10
• The Bulge Radial Velocity Assay for RR Lyrae stars (BRAVA-RR) DR2: a Bimodal Bulge?
• Metallicity-dependendent kinematics and morphology of the Milky Way bulge
• Age Demographics of the Milky Way Disk and Bulge
• Transverse kinematics of the Galactic bar-bulge from VVV and Gaia
• A machine learned classifier for RR Lyrae in the VVV survey
• The Stellar Halo in the Inner Milky Way: Predicted Shape and Kinematics
• Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics
• Forming disc galaxies in major mergers: III. The effect of angular momentum on the radial density profiles of disc galaxies
• Over 78 000 RR Lyrae Stars in the Galactic Bulge and Disk from the OGLE Survey

Cited by in corpus (14)

• The Milky Way bar and bulge revealed by APOGEE DR16 and Gaia EDR3
• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• Variable star classification across the Galactic bulge and disc with the VISTA Variables in the Vía Láctea survey
• BAYES-LOSVD: a bayesian framework for non-parametric extraction of the line-of-sight velocity distribution of galaxies
• Orbits of globular clusters computed with dynamical friction in the Galactic anisotropic velocity dispersion field
• Age-morphology dependence of the Milky Way boxy/peanut bulge seen in Mira variables
• Comparing bulge RR Lyrae stars with bulge giants -- Insight from 3D kinematics
• Probing the Milky Way stellar and brown dwarf initial mass function with modern microlensing observations
• The small boxy/peanut structure of the Milky Way traced by old stars
• VVV catalog of ab-type RR Lyrae in the inner Galactic bulge
• The Galactic Bulge exploration IV.: RR~Lyrae stars as traces of the Galactic bar -- 3D and 5D analysis, extinction variation
• Predicted Trends in Milky Way Bulge Proper Motion Rotation Curves: future Prospects for HST and LSST
• Unveiling VVV/WISE Mira variables on the far side of the Galactic disk: Distances, kinematics and a new extinction law
• An MCMC Approach to the Three-dimensional Structure of the Milky Way Bulge using OGLE-IV $\delta$ Scuti Stars