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

The rotation curve (RC) of the Milky Way out to ~ 100 kpc 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. To derive the RC, the PRCG sample of the warm disc population and the HKG sample of halo stellar population are respectively analyzed using a kinematical model allowing for the asymmetric drift corrections and re-analyzed using the spherical Jeans equation along with measurements of the anisotropic parameter β currently available. The typical uncertainties of RC derived from the PRCG and HKG samples are respectively 5-7 km/s and several tens km/s. We determine a circular velocity at the solar position, Vc (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. From the newly constructed RC, combined with other constraints, we have built a parametrized mass model for the Galaxy, yielding a virial mass of the Milky Way's dark matter halo of 0.90+0.07-0.08 × 10¹² M_ and a local dark matter density, ρ, dm = 0.32+0.02-0.02 GeV cm⁻³.