We present a kinematic analysis of a sample of 23,908 G- and K-type dwarfs in the Galactic disk .
Based on the \alpha -abundance ratio , [ \alpha /Fe ] , we separated our sample into low- \alpha thin-disk and high- \alpha thick-disk stars .
We find a V _ { \phi } gradient of –28.2 km s ^ { -1 } dex ^ { -1 } over [ Fe/H ] for the thin disk , and an almost flat trend of the velocity dispersions of V _ { R } , V _ { \phi } , and V _ { Z } components with [ Fe/H ] .
The metal-poor ( MP ; [ Fe/H ] < –0.3 ) thin-disk stars with low- V _ { \phi } velocities have high eccentricities ( e ) and small perigalacticon distances ( r _ { p } ) , while the high- V _ { \phi } MP thin-disk stars possess low e and large r _ { p } .
Interestingly , half of the super metal-rich ( [ Fe/H ] > + 0.1 ) stars in the thin disk exhibit low- e , solar-like orbits .
Accounting for the inhomogeneous metallicity distribution of the thin-disk stars with various kinematics requires radial migration by churning – it apparently strongly influences the current structure of the thin disk ; we can not rule out the importance of blurring for the high- e stars .
We derive a rotation velocity gradient of + 36.9 km s ^ { -1 } dex ^ { -1 } for the thick disk , and decreasing trends of velocity dispersions with increasing [ Fe/H ] .
The thick-disk population also has a broad distribution of eccentricity , and the number of high- e stars increases with decreasing [ Fe/H ] .
These kinematic behaviors could be the result of a violent mechanism , such as a gas-rich merger or the presence of giant turbulent clumps , early in the history of its formation .
Dynamical heating by minor mergers and radial migration may also play roles in forming the current thick-disk structure .