On the Kinematic Signature of the Galactic Warp As Revealed By the LAMOST-TGAS Data

Abstract

Using a sample of about 123,000 stars with accurate 3D velocity measurements from the LAMOST-TGAS data, we confirm the kinematic signature of the Galactic warp recently found by Schönrich & Dehnen. The data reveal a clear trend of increasing mean vertical velocity as a function of absolute vertical angular momentum L z and azimuthal velocity V ϕ for guiding center radius R g between 6.0 and 10.5 kpc. The trend is consistent with a large-scale Galactic warp. Similar to Schönrich & Dehnen, we also find a wave-like pattern of versus L z with an amplitude of ∼0.9 km s −1 on a scale of ∼2.0 kpc, which could arise from bending waves or a winding warp. Finally, we confirm a prominent, localized peak in near L z  ∼ 2150 kpc km s −1 (corresponding to R g ∼ 9 kpc and V ϕ ∼ 255 km s −1 ). The additional line-of-sight velocity information from LAMOST reveals that stars in this feature have a large, inward radial velocity of V R  ∼ −13.33 ± 0.59 km s −1 and a small radial velocity dispersion of σ R  ∼ 25.27 ± 0.89 km s −1 , suggesting that a stellar stream gives rise to this feature.