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

By Jo Bovy, Hans-Walter Rix. 2013

369 citations recorded by the source corpus.

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 < RGC < 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 < RGC < 9 kpc. Using metal-poor MAPs with small radial scale lengths as dynamical tracers probes 4.5 kpc ≲ RGC ≲ 7 kpc, while MAPs with longer radial scale lengths sample 7 kpc ≲ RGC ≲ 9 kpc. We measure the mass-weighted Galactic disk scale length to be Rd = 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: M* = 4.6 ± 0.3 + 3.0 (R0/ kpc − 8) × 1010 M☉ and a total local surface density of of which 38 ± 4 M☉ pc−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 Vc, disk/Vc, total = 0.83 ± 0.04 at R = 2.2 Rd. We also constrain for the first time the radial profile of the dark halo at such small Galactocentric radii, finding that ρDM(r; ≈R0)∝1/rα 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.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/043183a119f3d54b30ac5ddd99e9fa30fa7a75c1

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ETHOS - an effective theory of structure formation: dark matter physics as a possible explanation of the small-scale CDM problems (2015, neutral): “Such small cores in the MW galaxy (or Andromeda) are fully consistent with any constraints from observations (e.g. Bovy & Rix 2013).”
The milky way total mass profile as inferred from Gaia DR2 (2019, background): “…puzzle: previous measurements suggested that the MW rotation curve is dominated by the stellar component up to distances of R∼12− 14 kpc (e.g. Bovy & Rix 2013; Eilers et al. 2019), in disagreement with recent hydrodynamical simulations that find that the DM should already be dominant for R…”
Constraining the Galaxy's dark halo with RAVE stars (2014, methodology): “Bovy & Rix (2013) used quasi-isothermal DFs to derive the estimates of Kz plotted in Fig.”
TRIGONOMETRIC PARALLAXES OF HIGH MASS STAR FORMING REGIONS: THE STRUCTURE AND KINEMATICS OF THE MILKY WAY (2014, background): “…of Porcel et al. (1998) who modeled the positions and magnitudes of 700,000 stars in the Two Micron Galactic Survey database and found RD = 2.3 ± 0.3 kpc and, more recently, Bovy & Rix (2013), who modeled the dynamics of ≈ 16, 000 stars from the SEGUE survey and concluded that RD = 2.14± 0.14 kpc.”
The structure of the Milky Way's bar outside the bulge (2015, background): “Assuming that the surface density Σ is exponential Σ ∝ exp(R/Rd) then the surface density at Galactocentric radius 4kpc is a factor 7.4 higher than in the solar neighbourhood for Rd = 2.15kpc (Bovy & Rix 2013).”
Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution (2016, methodology): “Following Bovy & Rix (2013), we add the interstellar medium contribution to the potential by modelling it as an additional thin disk with scalelength hR,ism = 2× hR,∗ and scaleheight hR,ism = 130pc.”
THE SHAPE OF THE INNER MILKY WAY HALO FROM OBSERVATIONS OF THE PAL 5 AND GD–1 STELLAR STREAMS (2016, methodology): “The lower cut-off in c/a in all of these models happens because the FZ data from Bovy & Rix (2013) indicate a short scale length (≈ 2.5 kpc) for the total mass within ≈ 1 kpc of the disk mid-plane.”
galpy: A python LIBRARY FOR GALACTIC DYNAMICS (2014, methodology): “…(2πGM pc−2) and the local visible surface density Σ = 55 ± 5 M pc−2 from Zhang et al. (2013); 3. the vertical force measurements at 1.1 kpc from the plane of Bovy & Rix (2013); 4. the terminal-velocity measurements of Clemens (1985) and McClure-Griffiths & Dickey (2007), modeled in the same…”
Vertical disc heating in Milky Way-sized galaxies in a cosmological context (2015, background): “…ratio (D/T ) is listed in Table 1, which confirms the prominence of the stellar discs, and the present day radial scale length and bulge Sersic index reflect that the simulation suite contains a variety of discs similar in size and mass to that of the Milky Way (Rix & Bovy 2013; Bovy & Rix 2013).”
FORTY-SEVEN MILKY WAY-SIZED, EXTREMELY DIFFUSE GALAXIES IN THE COMA CLUSTER (2014, background): “Bovy & Rix (2013) derive a mass-weighted exponential scale length of 2.15± 0.14 kpc, corresponding toreff = 3.6 kpc. Twelve of the newly found objects are larger than this.”
The local dark matter density (2014, methodology): “Finally, I review results for a recent study that also uses the SDSS data, but slices the stars into narrow ‘Mono-Abundance Populations’ (MAPs) (Bovy & Rix, 2013).”
SDSS IV MaNGA – metallicity and nitrogen abundance gradients in local galaxies (2017, methodology): “/M ) = 10.8, Bovy & Rix 2013) based on the results of this work using the disc-only effective radius (Sec.”
Constraining the thick disc formation scenario of the Milky Way (2014, positive): “Article number, page 15 of 24page.24 Most recently, Bovy & Rix (2013) estimated on the ground of the rotation curve that the total scale length of the disc is 2.15 kpc, which agrees very well with our two populations of thin and thick disc.”
THE APOGEE RED-CLUMP CATALOG: PRECISE DISTANCES, VELOCITIES, AND HIGH-RESOLUTION ELEMENTAL ABUNDANCES OVER A LARGE AREA OF THE MILKY WAY'S DISK (2014, methodology): “Using current measurements of the distribution of stellar mass (Bovy & Rix 2013), 80% of the stars in the Milky Way disk lie at R R0 and |Z| 1 kpc, where R0 is the distance from the Sun to the Galactic center and R and Z are Galactocentric cylindrical coordinates.”
The APOSTLE simulations: solutions to the Local Group's cosmic puzzles (2015, result): “…substructures, the stellar masses of the MW and M31 analogues in our simulations lie in the range 1.5–5.5 × 1010 M , on the low end compared to the observational estimates for the MW [5 × 1010 M (Flynn et al. 2006; Bovy & Rix 2013)] but lower than those for M31 [1011 M (Tamm et al. 2012)].”