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 ± 0.079syst 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.

Efficient solution of the anisotropic spherically aligned axisymmetric Jeans equations of stellar hydrodynamics for galactic dynamics

“…This theoretical expectation was confirmed by recent Gaia studies which found that the velocity ellipsoid is well approximated by an alignment with the spherical polar coordinate system, both in the outer stellar halo (Wegg et al 2019) and in the disk region (Hagen et al 2019;Everall et al 2019). These data motivates the development of a practically-usable spherically-aligned solution for the Jeans equations, which we already successfully applied to the Gaia data (Nitschai et al 2019).…”

“…This method has already been applied to model the Gaia DR2 data, where we found it describes the observations remarkably well with minimal freedom and good accuracy (Nitschai et al 2019). I leave further applications to real data to future studies.…”

Disc dichotomy signature in the vertical distribution of [Mg/Fe] and the delayed gas infall scenario

“…We integrate stellar orbits for different SSPs(τ) using the galpy 3 package subject to the MWPotential2014 gravitational potential (Bovy 2015). For the rotational velocity v T at the so-3 http://github.com/jobovy/galpy lar distance R we use the one computed by Ablimit et al (2020) applying the three-dimensional velocity vector method for Cepheids (v T = 232.5 ± 0.83 km s −1 ) that is consistent with the most recent estimation by Nitschai et al (2021) with a dynamical model of the Milky Way using APOGEE and Gaia data. The initial vertical velocity for the SSP v 0,z (τ) born at the evolutionary time t B = t G − τ has been chosen by satisfying the following condition:…”

Spiral density-wave structure parameters in the solar neighbourhood derived from longitudinal velocities of Gaia EDR3 OB stars: 3D approach

“…We find V circ,0 ≡ r 0 0 ≈ 241 km s −1 . This value of the circular velocity is just slightly greater than the values V circ,0 ≈ 233 km s −1 , V circ,0 ≈ 229 km s −1 , V circ,0 ≈ 234 km s −1 , V circ,0 ≈ 239 km s −1 , and V circ,0 ≈ 235 km s −1 measured by McMillan (2017), Eilers et al (2020), Mróz et al (2019), VERA Collaboration (2020), and Nitschai et al (2021), respectively, adopting the fundamental axisymmetric model.…”