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Title: A direct dynamical measurement of the Milky Way's disk surface density profile, disk scale length, and dark matter profile at 4 kpc ≲ R ≲ 9 kpc

We present and apply rigorous dynamical modeling with which we infer unprecedented constraints on the stellar and dark matter mass distribution within our Milky Way (MW), based on large sets of phase-space data on individual stars. Specifically, we model the dynamics of 16,269 G-type dwarfs from SEGUE, which sample 5 kpc < R{sub GC} < 12 kpc and 0.3 kpc ≲ |Z| ≲ 3 kpc. We independently fit a parameterized MW potential and a three-integral, action-based distribution function (DF) to the phase-space data of 43 separate abundance-selected sub-populations (MAPs), accounting for the complex selection effects affecting the data. We robustly measure the total surface density within 1.1 kpc of the mid-plane to 5% over 4.5 kpc < R{sub GC} < 9 kpc. Using metal-poor MAPs with small radial scale lengths as dynamical tracers probes 4.5 kpc ≲ R{sub GC} ≲ 7 kpc, while MAPs with longer radial scale lengths sample 7 kpc ≲ R{sub GC} ≲ 9 kpc. We measure the mass-weighted Galactic disk scale length to be R{sub d} = 2.15 ± 0.14 kpc, in agreement with the photometrically inferred spatial distribution of stellar mass. We thereby measure dynamically the mass of the Galactic stellar disk to unprecedented accuracy:more » M {sub *} = 4.6 ± 0.3 + 3.0 (R {sub 0}/ kpc – 8) × 10{sup 10} M {sub ☉} and a total local surface density of Σ{sub R{sub 0}}(Z=1.1 kpc)=68 ± 4 M{sub ⊙} pc{sup −2} of which 38 ± 4 M {sub ☉} pc{sup –2} is contributed by stars and stellar remnants. By combining our surface density measurements with the terminal velocity curve, we find that the MW's disk is maximal in the sense that V {sub c,} {sub disk}/V {sub c,} {sub total} = 0.83 ± 0.04 at R = 2.2 R{sub d} . We also constrain for the first time the radial profile of the dark halo at such small Galactocentric radii, finding that ρ{sub DM}(r; ≈R {sub 0})∝1/r {sup α} with α < 1.53 at 95% confidence. Our results show that action-based DF modeling of complex stellar data sets is now a feasible approach that will be fruitful for interpreting Gaia data.« less
Authors:
 [1] ;  [2]
  1. Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States)
  2. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
Publication Date:
OSTI Identifier:
22348451
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ACCOUNTING; ACCURACY; CARBON 12; DENSITY; DISTRIBUTION FUNCTIONS; LIMITING VALUES; MAPS; MASS; MASS DISTRIBUTION; METALS; MILKY WAY; NITROGEN 15; NONLUMINOUS MATTER; PHASE SPACE; SIMULATION; STARS; SURFACES