Dynamical Model of the Milky Way Using APOGEE and Gaia Data

Abstract

We construct a dynamical model of the Milky Way disk from a data set that combines Gaia EDR3 and APOGEE data throughout galactocentric radii in the range 5.0 kpc ≤ R ≤ 19.5 kpc. We make use of the spherically aligned Jeans anisotropic method to model the stellar velocities and their velocity dispersions. Building upon our previous work, our model is now fitted to kinematic maps that have been extended to larger galactocentric radii due to the expansion of our data set, probing the outer regions of the Galactic disk. Our best-fitting dynamical model suggests a logarithmic density slope of α DM = −1.602 ± 0.079 syst for the dark matter halo and a dark matter density of ρ DM ( R ⊙ ) = (8.92 ± 0.56 syst ) × 10 −3 M ⊙ pc −3 (0.339 ± 0.022 syst GeV cm 3 ). We estimate a circular velocity at the solar radius of v circ = (234.7 ± 1.7 syst ) km s −1 with a decline toward larger radii. The total mass density is ρ tot ( R ⊙ ) = (0.0672 ± 0.0015 syst ) M ⊙ pc −3 with a slope of α tot = −2.367 ± 0.047 syst for 5 kpc ≤ R ≤ 19.5 kpc, and the total surface density is Σ( R ⊙ , ∣ z ∣ ≤ 1.1 kpc) = (55.5 ± 1.7 syst ) M ⊙ pc −2 . While the statistical errors are small, the error budget of the derived quantities is dominated by the three to seven times larger systematic uncertainties. These values are consistent with our previous determination, but the systematic uncertainties are reduced due to the extended data set covering a larger spatial extent of the Milky Way disk. Furthermore, we test the influence of nonaxisymmetric features on our resulting model and analyze how a flaring disk model would change our findings.