Kinematics of the Galactic disk from LAMOST Dwarf sample

TL;DR

This study analyzes the kinematics and metallicity of over 130,000 dwarf stars from LAMOST and SDSS to understand the structure and formation of the Galactic disk, highlighting differences between thin and thick disk populations.

Contribution

It provides new insights into the metallicity-velocity relationships and orbital eccentricity distributions, supporting the gas-rich merger model for thick-disk formation.

Findings

Negative metallicity-rotation velocity gradient in thin disk

Positive gradient in thick disk

Eccentricity distribution peaks at low e, consistent with merger models

Abstract

Based on the LAMOST survey and Sloan Digital Sky Survey (SDSS), we use low-resolution spectra of 130,043 F/G-type dwarf stars to study the kinematics and metallicity properties of the Galactic disk. Our study shows that the stars with poorer metallicity and larger vertical distance from Galactic plane tend to have larger eccentricity and velocity dispersion. After separating the sample stars into likely thin-disk and thick-disk sub-sample, we find that there exits a negative gradient of rotation velocity $V_{\phi}$ with metallicity [Fe/H] for the likely thin-disk sub-sample, and the thick-disk sub-sample exhibit a larger positive gradient of rotation velocity with metallicity. By comparing with model prediction, we consider the radial migration of stars appears to have influenced on the thin-disk formation. In addition, our results shows that the observed thick-disk stellar orbital eccentricity distribution peaks at low eccentricity ($e \sim 0.2$) and extends to a high eccentricity ($e \sim 0.8$). We compare this result with four thick-disk formation simulated models, and it imply that our result is consistent with gas-rich merger model.