2012ApJ...759..131B

We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc ≲ R ≲ 14 kpc from the first year of data from the Apache Point Observatory Galactic Evolution Experiment. We model the line-of-sight velocities of 3365 stars in 14 fields with b = 0° between 30° ≤ l ≤ 210° out to distances of 10 kpc using an axisymmetric kinematical model that includes a correction for the asymmetric drift of the warm tracer population (σ_ R_~ 35 km/s). We determine the local value of the circular velocity to be V_c(R₀) = 218±6 km/s and find that the rotation curve is approximately flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also measure the Sun's position and velocity in the Galactocentric rest frame, finding the distance to the Galactic center to be 8 kpc < R₀< 9 kpc, radial velocity V_R, ☉_= -10±1 km/s, and rotational velocity V_φ, ☉_= 242⁺¹⁰_- 3_ km/s, in good agreement with local measurements of the Sun's radial velocity and with the observed proper motion of Sgr A*. We investigate various systematic uncertainties and find that these are limited to offsets at the percent level, ∼2 km/s in V_c. Marginalizing over all the systematics that we consider, we find that V_c(R₀) < 235 km/s at >99 % confidence. We find an offset between the Sun's rotational velocity and the local circular velocity of 26±3 km/s, which is larger than the locally measured solar motion of 12 km/s. This larger offset reconciles our value for V_c with recent claims that V_c ≳ 240 km/s. Combining our results with other data, we find that the Milky Way's dark-halo mass within the virial radius is ∼8 x10¹¹ M_☉.