The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution

Image: This annotated artist’s impression shows the Milky Way galaxy. The blue halo of material surrounding the galaxy indicates the expected distribution of the mysterious dark matter. Credit: ESO/L. Calçada

In a recent paper (Huang et al. 2016) the rotation curve (RC) of the Milky Way out to ~100kpc has been constructed using ~16,000 primary red clump giants (PRCGs) in the outer disk selected from the LSS-GAC and the SDSS-III/APOGEE survey, combined with ~5700 halo K giants (HKGs) selected from the SDSS/SEGUE survey.

The authors determine a circular velocity at the solar position, V_c(R₀)=240±6 km/s and an azimuthal peculiar speed of the Sun, V_⊙=12.1±7.6 km/s, both in good agreement with the previous determinations.

The newly constructed RC has a generally flat value of 240 km/s within a Galactocentric distance r of 25 kpc and then decreases steadily to 150 km/s at r~100 kpc.

On top of this overall trend, the RC exhibits two prominent localized dips, one at r~11 kpc and another at r~19 kpc. The dips could be explained by assuming the existence of two massive (dark) matter rings in the Galactic plane.

From the newly constructed RC, combined with other data, the authors have built a parametrized mass model for the Galaxy, yielding a virial mass of the Milky Way's dark matter halo of ~0.90×10¹² M_⊙ and a total disc mass of ~ 4.32×10¹⁰M_⊙.

The model yields a local dark matter density, ρ_⊙,dm ~ 0.32 GeV cm⁻³, which again agrees well with the previous determinations.

Huang et al. 2016 - The Milky Way's rotation curve out to 100 kpc and its constraint on the Galactic mass distribution - (arXiv)

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