Torus Models of the Outer Disc of the Milky Way using LAMOST Survey Data

Abstract

With a sample of 48,161 K giant stars selected from the LAMOST DR 2 catalogue, we construct torus models in a large volume extending, for the first time, from the solar vicinity to a Galactocentric distance of $\sim 20$ kpc, reaching the outskirts of the Galactic disc. We show that the kinematics of the K giant stars match conventional models, e.g. as created by Binney in 2012, in the Solar vicinity. However such two-disc models fail if they are extended to the outer regions, even if an additional disc component is utilised. If we loosen constraints in the Sun's vicinity, we find that an effective thick disc model could explain the anti-centre of the MW. The LAMOST data imply that the sizes of the Galactic discs are much larger, and that the outer disc is much thicker, than previously thought, or alternatively that the outer structure is not a conventional disc at all. However, the velocity dispersion ${\sigma }_{0z}$ of the kinematically thick disc in the best-fitting model is about 80 km s${}^{-1}$ and has a scale parameter $R_{\sigma }$ for an exponential distribution function of $\sim 19$ kpc. Such a height ${\sigma }_{0z}$ is strongly rejected by current measurements in the solar neighbourhood, and thus a model beyond quasi-thermal, two or three thin or thick discs is required.

11 pages, 7 figures and 3 tables, Accepted for publication in MNRAS

References in corpus (19)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• galpy: A Python Library for Galactic Dynamics
• The Radial Velocity Experiment (RAVE): first data release
• The GALAH Survey: Scientific Motivation
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• Rings and Radial Waves in the Disk of the Milky Way
• On the Shoulders of Giants: Properties of the Stellar Halo and the Milky Way Mass Distribution
• Constraining the Galaxy's dark halo with RAVE stars
• Made-to-Measure models of the Galactic Box/Peanut bulge: stellar and total mass in the bulge region
• APOGEE: The Apache Point Observatory Galactic Evolution Experiment
• ARGOS II: The Galactic Bulge Survey
• Estimating distances from parallaxes. III. Distances of two million stars in the Gaia DR1 catalogue
• The Bulge Radial Velocity Assay (BRAVA): I. Techniques and a Rotation Curve
• A radial age gradient in the geometrically thick disk of the Milky Way
• Disassembling the Galaxy with angle-action coordinates
• The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
• Estimation of distances to stars with stellar parameters from LAMOST
• A fast algorithm for estimating actions in triaxial potentials
• The local spiral arm in the LAMOST-Gaia common stars?

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• Classifying globular clusters and applying them to estimate the mass of the Milky Way
• The Data Processing of the LAMOST Medium-Resolution Spectral Survey of Galactic Nebulae (LAMOST MRS-N Pipeline)
• Dynamical Models of the Milky Way in Action Space with LAMOST DR8 and GAIA EDR3