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

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 of Q. Wang et al. did not include Gaia data, making them incompatible with the new sample’s proper motion distributions. 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 an MW virial mass of 1.35 × 10 12 M ⊙ , a local stellar density of 0.0696 M ⊙ pc −3 , and a local dark matter density of 0.0115 M ⊙ pc −3 . Our main conclusion supports a thicker and more extended thick disk, alongside a cooler thin disk, compared to the best-fitting model of Q. Wang et al. Near the Sun, our model aligns well with observations, but it 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.