Date Published:

November 1, 2012

Abstract:

We measure the Milky Way's rotation curve over the Galactocentric range4 kpc <~ R <~ 14 kpc from the first year of data from the ApachePoint Observatory Galactic Evolution Experiment. We model theline-of-sight velocities of 3365 stars in 14 fields with b = 0°between 30° <= l <= 210° out to distances of 10 kpc usingan axisymmetric kinematical model that includes a correction for theasymmetric drift of the warm tracer population (σ _R ≈ 35 km s^-1). We determine the local value of thecircular velocity to be V_c (R ₀) = 218 ± 6km s^-1 and find that the rotation curve isapproximately flat with a local derivative between -3.0 kms^-1 kpc^-1 and 0.4 kms^-1 kpc^-1. We also measure the Sun'sposition and velocity in the Galactocentric rest frame, finding thedistance to the Galactic center to be 8 kpc < R ₀ < 9kpc, radial velocity V _{R, &sun;} = -10 ± 1 kms^-1, and rotational velocity V _{phi, &sun;}= 242⁺¹⁰ _{- 3} km s^-1, ingood agreement with local measurements of the Sun's radial velocity andwith the observed proper motion of Sgr A*. We investigate varioussystematic uncertainties and find that these are limited to offsets atthe percent level, ~2 km s^-1 in V_c .Marginalizing over all the systematics that we consider, we find thatV_c (R ₀) < 235 km s^-1 at

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