Quantifying chemical and kinematical properties of Galactic disks
  We aim to quantify the chemical and kinematical properties of the Galactic
disks with a sample of 119,558 giant stars having abundances and 3D velocities
taken or derived from the APOGEE DR17 and Gaia EDR3 catalogs. The Gaussian
Mixture Model is employed to distinguish the high-$\alpha$ and low-$\alpha$
sequences along the metallicity by simutaneously using the chemical and
kinematical data. Four disk components are identified and quantified that named
as h$\alpha$mp, h$\alpha$mr, l$\alpha$mp, and l$\alpha$mr disks, which
correspond to the features of high-$\alpha$ or low-$\alpha$, and metal-poor or
metal-rich. Combined with the spatial and stellar age information, we confirm
that they are well interpreted in the two-infall formation model. The first
infall of turbulent gas quickly forms the hot and thick h$\alpha$mp disk with
consequent thinner h$\alpha$mr and l$\alpha$mr disks. Then the second gas
accretion forms a thinner and outermost l$\alpha$mp disk. We find that the
inside-out and upside-down scenario does not only satisfy the overall Galactic
disk formation of these two major episodes, but also presents in the formation
sequence of three inner disks. Importantly, we reveal the inverse Age-[M/H]
trend of the l$\alpha$mr disk, which means its younger stars are more
metal-poor, indicating that the rejuvenate gas from the second accretion
gradually dominates the later star formation. Meanwhile, the recently formed
stars convergence to [M/H]$\sim$-0.1 dex, demonstrating a sufficiently mixture
of gas from two infalls.
