Dynamical Models of the Milky Way in Action Space with LAMOST DR8 and GAIA EDR3

TL;DR

This study refines dynamical models of the Milky Way using extensive star data from LAMOST and Gaia, providing new insights into its mass, density, and disk structure, with implications for understanding Galactic dynamics.

Contribution

It develops improved action-based, self-consistent Milky Way models incorporating Gaia data, enhancing previous models and constraining key Galactic parameters.

Findings

Estimated Milky Way virial mass: 1.35 x 10^12 M_sun

Local dark matter density: 0.0115 M_sun/pc^3

Thicker, more extended thick disk suggested

Abstract

This work explores dynamical models of the Milky Way (MW) by analyzing a sample of 86,109 K giant stars selected through cross-matching the LAMOST DR8 and Gaia EDR3 surveys. Our earlier torus models in Wang et al. (2017) did not include Gaia data, making them incompatible with the new proper motion distributions of samples. Here, we refine the construction of action-based, self-consistent models to constrain the three-dimensional velocity distribution of K giants over a larger parameter space, drawing on a series of existing MW models. This approach produces several new MW models. Our best-fit model for the local kinematics near the Sun indicates a MW virial mass of 1.35 $\times 10^{12} M_\odot$, a local stellar density of 0.0696 $\rm M_\odot pc^{-3}$, and a local dark matter density of 0.0115 $\rm M_\odot pc^{-3}$. Our main conclusion supports a thicker and more extended thick disk, alongside a cooler thin disk, compared to the best-fitting model in Wang et al. (2017). Near the Sun, our model aligns well with observations, but is less satisfactory at distances far from the Galactic center, perhaps implying unidentified structures. Further high-precision observations will be critical for understanding the dynamics in these outer Galactic regions, and will require a more realistic model.