We construct the first comprehensive dynamical model for the high-quality subset of stellar kinematics of the Milky Way disc, with full 6D phase-space coordinates, provided by the Gaia Data Release 2. We adopt an axisymmetric approximation and use an updated Jeans Anisotropic Modelling method, which allows for a generic shape and radial orientation of the velocity ellipsoid, as indicated by the Gaia data, to fit the mean velocities and all three components of the intrinsic velocity dispersion tensor. The Milky Way is the first galaxy for which all intrinsic phase space coordinates are available, and the kinematics are superior to the best integral-field kinematics of external galaxies. This situation removes the long-standing dynamical degeneracies and makes this the first dynamical model highly over-constrained by the kinematics. For these reasons, our ability to fit the data provides a fundamental test for both galaxy dynamics and the mass distribution in the Milky Way disc. We tightly constrain the average total density logarithmic slope, in the radial range 3.6-12 kpc, to be α tot = −2.149 ± 0.055 and find that the dark halo slope must be significantly steeper than α DM = −1 (NFW). The dark halo shape is close to spherical and its density is ρ DM (R ) = 0.0115 ± 0.0020 M pc −3 (0.437 ± 0.076 GeV cm −3 ), in agreement with previous estimates. The circular velocity at the solar position v circ R = 236.5 ± 3.1 km s −1 (including systematics) and its radial trends are also consistent with recent determinations.

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 ± 0.079syst for the dark matter halo and a dark matter density of ρ DM(R ⊙) = (8.92 ± 0.56syst) × 10−3 M ⊙ pc−3 (0.339 ± 0.022syst GeV cm3). We estimate a circular velocity at the solar radius of v circ = (234.7 ± 1.7syst) km s−1 with a decline toward larger radii. The total mass density is ρ tot(R ⊙) = (0.0672 ± 0.0015syst) M ⊙ pc−3 with a slope of α tot = −2.367 ± 0.047syst for 5 kpc ≤ R ≤ 19.5 kpc, and the total surface density is Σ(R ⊙, ∣z∣ ≤ 1.1 kpc) = (55.5 ± 1.7syst) 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.

In this paper we simultaneously fit the orbits and line-of-sight velocities of the ionized gas around the supermassive black hole, Sagittarius A* (Sgr A*), at the center of the Milky Way. The data we use are taken with the K-band Multi Object Spectrograph (KMOS), presented in Feldmeier-Krause et al., and cover the central ∼2 pc of the Milky Way. From the brightest gas emission line in the K-band, the Brγ line, we derive the spatial distribution and line-of-sight velocities of the gas in the minispiral. Using the flux distribution and the line-of-sight velocity information, we perform a fit to the three main gas streamers in the minispiral, the Northern Arm, Eastern Arm, and Western Arc, using a Bayesian modeling method, and are able to reconstruct the three-dimensional orbits of these gas streamers. With the best-fit orbital parameters and the measured line-of-sight velocities, we constrain the mass of Sgr A*. The orbit of the Eastern Arm is the one that is best constrained using our data. It gives a best-fit orbital period of yr and results in an enclosed mass of