KINEMATICS OF THE STELLAR HALO AND THE MASS DISTRIBUTION OF THE MILKY WAY USING BLUE HORIZONTAL BRANCH STARS

By P. Kafle, Sanjib Sharma, Geraint F. Lewis, Joss Bland-Hawthorn. 2012

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Here, we present a kinematic study of the Galactic halo out to a radius of ∼60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates (σr, σθ, σϕ) and the anisotropy profile (β). The radial velocity dispersion profile (σr) is measured out to a galactocentric radius of r ∼ 60 kpc, but due to the lack of proper-motion information, σθ, σϕ, and β could only be derived directly out to r ∼ 25 kpc. From a starting value of β ≈ 0.5 in the inner parts (9 < r/kpc < 12), the profile falls sharply in the range r ≈ 13–18 kpc, with a minimum value of β = −1.2 at r = 17 kpc, rising sharply at larger radius. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of β ≈ 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (vcirc) of the Galaxy out to r ∼ 25 kpc. The mass of the Galaxy within r ≲ 25 kpc is determined to be 2.1 × 1011 M☉, and with a three-component fit to vcirc(r), we determine the virial mass of the Milky Way dark matter halo to be Mvir = 0.9+0.4−0.3 × 1012 M☉ (Rvir = 249+34−31 kpc).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/cf379d18b2c5f8ec8bf453062c39c1a14f4db8e4

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Citations in the corpus

The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution (2016, methodology): “As mentioned above, the latter is also seen in the RC derived by Kafle et al. (2012) using over 4000 BHB stars.”
Co-formation of the disc and the stellar halo (2018, unknown): “For slightly larger volumes probed with somewhat more luminous tracers, similar values of β ∼ 0.5 were obtained (see e.g. Deason et al. 2012; Kafle et al. 2012).”
Evidence for an Intermediate-mass Milky Way from Gaia DR2 Halo Globular Cluster Motions (2018, methodology): “Kafle et al. (2012) estimated M(< 25 kpc) ≈ 0.21 × 1012 M , unfortunately without uncertainties, by analysing blue horizontal branch stars in the halo, and Küpper et al. (2015) estimated M(< 19 kpc) = 0.21 ± 0.04 × 1012 M by analysing the orbit of the Palomar 5 tidal stream, both in good agreement…”
The RAVE survey : the Galactic escape speed and the mass of the Milky Way (2013, methodology): “This model changes the values for the circular speed (223 km s−1 and 264 km s−1 for the unaltered and the contracted cases, respectively) but not the consistency with the mass estimates by Kafle et al. (2012), Gnedin et al. (2010), or Xue et al. (2008).”
ON THE SHOULDERS OF GIANTS: PROPERTIES OF THE STELLAR HALO AND THE MILKY WAY MASS DISTRIBUTION (2014, methodology): “One preferred approach (Battaglia et al. 2005; Xue et al. 2008; Kafle et al. 2012) with the Jeans Analysis is to decompose the Galaxy into its dominant components (disk, bulge and halo).”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “They normalize the dark matter halo to the density profile and total mass inferred from the kinematics of halo stars (Kafle et al. 2012).”
The milky way total mass profile as inferred from Gaia DR2 (2019, methodology): “…total mass of the Galactic DM halo using a variety of methods, such as the dynamics of the stellar halo (e.g. Xue et al. 2008; Deason et al. 2012; Kafle et al. 2012), globular clusters (e.g. Eadie & Harris 2016; Posti & Helmi 2019; Watkins et al. 2019) and satellite galaxies (e.g. Watkins et al.…”