Understanding the velocity distribution of the Galactic Bulge with APOGEE and Gaia

Abstract

We revisit the stellar velocity distribution in the Galactic bulge/bar region with APOGEE DR16 and {\it Gaia} DR2, focusing in particular on the possible high-velocity (HV) peaks and their physical origin. We fit the velocity distributions with two different models, namely with Gauss-Hermite polynomial and Gaussian mixture model (GMM). The result of the fit using Gauss-Hermite polynomials reveals a positive correlation between the mean velocity ($\bar{V}$) and the "skewness" ($h_3$) of the velocity distribution, possibly caused by the Galactic bar. The $n=2$ GMM fitting reveals a symmetric longitudinal trend of $|{\mu }_2|$ and ${\sigma }_2$ (the mean velocity and the standard deviation of the secondary component), which is inconsistent to the $x_2$ orbital family predictions. Cold secondary peaks could be seen at $|l|\sim 6^{\circ }$. However, with the additional tangential information from {\it Gaia}, we find that the HV stars in the bulge show similar patterns in the radial-tangential velocity distribution ($V_{\mathrm{R}}-V_{\mathrm{T}}$), regardless of the existence of a distinct cold HV peak. The observed $V_{\mathrm{R}}-V_{\mathrm{T}}$ (or $V_{\mathrm{GSR}}-{\mu }_l$) distributions are consistent with the predictions of a simple MW bar model. The chemical abundances and ages inferred from ASPCAP and CANNON suggest that the HV stars in the bulge/bar are generally as old as, if not older than, the other stars in the bulge/bar region.

arXiv comment17 pages,13 figures

References in corpus (50)

• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• Local Kinematics and the Local Standard of Rest
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• Mass models of the Milky Way
• The Data Reduction Pipeline for the Apache Point Observatory Galactic Evolution Experiment
• First GLIMPSE Results on the Stellar Structure of the Galaxy
• Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars
• The Cannon: A data-driven approach to stellar label determination
• The Structure of the Milky Way's Bar Outside the Bulge
• Our Milky Way as a Pure-Disk Galaxy -- A Challenge for Galaxy Formation
• ARGOS III: Stellar Populations in the Galactic Bulge of the Milky Way
• The Second APOKASC Catalog: The Empirical Approach
• Red giant masses and ages derived from carbon and nitrogen abundances
• The Bulge Radial Velocity Assay (BRAVA): II. Complete Sample and Data Release
• Chemodynamical history of the Galactic Bulge
• Color-Magnitude Diagram Distribution of the Bulge Red Clump Stars - Evidence for the Galactic Bar
• Spectroscopic determination of masses (and implied ages) for red giants
• Bar Diagnostics in Edge-On Spiral Galaxies. III. N-Body Simulations of Disks
• 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
• Gas flow in barred potentials - III. Effects of varying the Quadrupole
• A Distinct Structure Inside the Galactic Bar
• Gas dynamics in the Milky Way: a low pattern speed model
• Constraining Metallicity-dependent Mixing and Extra Mixing using [C/N] in Alpha-Rich Field Giants
• APOGEE Kinematics I: Overview of the Kinematics of the Galactic Bulge as Mapped by APOGEE
• 2D kinematic signatures of boxy/peanut bulges
• The Apache Point Observatory Galactic Evolution Experiment: First Detection of High Velocity Milky Way Bar Stars
• Discovery of a Metal-Poor Field Giant with a Globular Cluster Second-Generation Abundance Pattern
• Inversion of stellar statistics equation for the Galactic Bulge
• Metallicity and kinematics of the bar in-situ
• Origin of the high v_los feature in the Galactic bar
• Globular clusters in the inner Galaxy classified from dynamical orbital criteria
• The Bulge Metallicity Distribution from the APOGEE Survey
• Kinematics in the Galactic Bulge with APOGEE: II. High-Order Kinematical Moments and Comparison to Extragalactic Bar Diagnostics
• What the Milky Way bulge reveals about the initial metallicity gradients in the disc
• A Kiloparsec-Scale Nuclear Stellar Disk in the Milky Way as a Possible Explanation of the High Velocity Peaks in the Galactic Bulge
• Resonant Orbits and the High Velocity Peaks Towards the Bulge
• The age distribution of stars in the Milky Way bulge
• SiO Masers in the Galactic Bulge and Disk: Kinematics from the BAaDE Survey
• Are high velocity peaks in the Milky Way bulge due to the bar?
• Theoretical Models of the Galactic Bulge
• Predicted Stellar Kinematics of a Kiloparsec-Scale Nuclear Disc (or Ring) in the Milky Way
• Chemical abundances and ages of the bulge stars in APOGEE high-velocity peaks
• Models of Bars with Exponential Density Profiles

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