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 \overline{{V}_z} 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 \overline{{V}_z} 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 \overline{{V}_z} 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.