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 found by Schönrich & Dehnen recently. 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 $V_{\ddot{I}}•$ 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 $\sim 0.9$ km s${}^{-1}$ on a scale of $\sim 2.0$ kpc, which could arise from bending waves or a winding warp. Finally, we confirm a prominent, localized peak in $\overline{V_z}$ near $L_z\sim 2150$ kpc km s${}^{-1}$ (corresponding to $R_g\sim 9$ kpc and $V_{\ddot{I}}•\sim 255$ 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 $V_R\sim -13.33\pm 0.59$ km s${}^{-1}$ and a small radial velocity dispersion $\ddot{I}{ƒ}_R\sim 25.27\pm 0.89$ km s${}^{-1}$, suggesting that a stellar stream gives rise to this feature.

ApJ accepted, 7 pages, 6 figures