Chemo-kinematic constraints on the Solar-neighborhood disk using 1.5 million LAMOST-Gaia FGK dwarf stars

Abstract Understanding the evolutionary history of the Milky Way disk remains a fundamental challenge in Galactic Astronomy, and unravelling this history requires a detailed analysis of disk stars. Utilizing large samples of non‑repetitive Solar-neighborhood F-, G- and K-type dwarfs with precise atmospheric and kinematic parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (\textit{LAMOST}) and the \textit{Gaia} surveys, we investigate these evolutionary mechanisms through a comprehensive chemo-kinematic analysis. We select thick- and thin-disk stars using two independent criteria (i.e., kinematic and chemical). The kinematic approach identifies 116,039 thick-disk and 1,302,598 thin-disk stars, whereas the chemical method yields 9,181 thick-disk and 1,361,453 thin-disk stars. We find that within Galactic heights of $0<|Z_{\rm GC}|<1.5\,{\rm kpc}$, thin-disk stars exhibit negative $[\rm{Fe}/\rm{H}]$ gradients, which become flatter (less negative) with increasing $|Z_{\rm GC}|$. This trend is recovered under both classification schemes. We also find that stars sharing similar kinematics do not possess identical chemical compositions across the $[\alpha/\rm{Fe}]$ versus $[\rm{Fe}/\rm{H}]$ plane, and that the orbital eccentricity distribution of thick-disk stars prominently peaks at $e = 0.2$-$0.4$. Our results indicate that radial migration contributes more to the evolution of the Galactic thin disk, while radial migration and gas-rich mergers contribute more to the thick disk.