Kinematics of the Galactic disc from a LAMOST dwarf sample.

Based on the LAMOST survey and Sloan Digital Sky Survey, we use low-resolution spectra of 130 043 F/G-type dwarf stars to study the kinematics and metallicity properties of the Galactic disc. Our study shows that the stars with poorer metallicity and larger vertical distance from the Galactic plane tend to have a larger eccentricity and velocity dispersion. After separating the sample stars into likely thin-disc and thick-disc sub-samples, we find that there exists a negative gradient of rotation velocity Vφ with metallicity [Fe/H] for the likely thin-disc subsample, and the thick-disc sub-sample exhibits a larger positive gradient of rotation velocity with metallicity. By comparing with model predictions, we consider that the radial migration of stars appears to have influenced the formation of the thin disc. In addition, our results show that the observed thick-disc stellar orbital eccentricity distribution peaks at low eccentricity (e ~ 0.2) and extends to a high eccentricity (e ~ 0.8). We compare this result with four thickdisc formation simulation models, which imply that our result is consistent with the gas-rich merger model. [ABSTRACT FROM AUTHOR]