Solar Neighborhood Kinematics from Gaia -LAMOST Dwarf Stars

Abstract

We use high-precision kinematic data from Gaia data release 2 (DR2) and spectroscopic data from Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) data release 5 (DR5) to explore the kinematics of solar neighborhood dwarf stars in the northern and southern sides of the Galactic plane. The metallicity range of the sampled stars is -0.5 < [Fe/H] < 0.5. Systematic north-south asymmetries in stellar radial motion and rotation are detected: stars in the north disk are moving toward the outer disk, while stars in the south disk have inward-streaming motion toward the Galactic center; stars in the north disk rotate slower than stars in the south disk in general. The tilt angle is antisymmetric about the Galactic plane: for an assumed Galactocentric distance of the Sun, R ₀ = 8.122 kpc, the increase in the tilt angle α _Rz with the vertical distance z is well described by the relation {α }_{Rz}=(1.11+/- 0.11)\arctan (z/{R}₀)-(0.0069+/- 0.0034). The variation of stellar kinematics with the vertical distance to the Galactic plane has no essential dependence on the metallicity.