Origin of chemical and dynamical properties of the Galactic thick disk
  We adopt a scenario in which the Galactic thick disk was formed by minor
merging between the first generation of the Galactic thin disk (FGTD) and a
dwarf galaxy about 9 Gyr ago and thereby investigate chemical and dynamical
properties of the Galactic thick disk. In this scenario, the dynamical
properties of the thick disk have long been influenced both by the mass growth
of the second generation of the Galactic thin disk (i.e., the present thin
disk) and by its non-axisymmetric structures. On the other hand, the early star
formation history and chemical evolution of the thin disk was influenced by the
remaining gas of the thick disk. Based on N-body simulations and chemical
evolution models, we investigate the radial metallicity gradient, structural
and kinematical properties, and detailed chemical abundance patterns of the
thick disk. Our numerical simulations show that the ancient minor merger event
can significantly flatten the original radial metallicity gradient of the FGTD,
in particular, in the outer part, and also can be responsible for migration of
inner metal-rich stars into the outer part (R>10kpc). The simulations show that
the central region of the thick disk can develop a bar due to dynamical effects
of a separate bar in the thin disk. The simulated orbital eccentricity
distributions in the thick disk for models with higher mass-ratios (~0.2) and
lower orbital eccentricities (~ 0.5) of minor mergers are in good agreement
with the corresponding observations. The simulated V_{phi}-|z| relation of the
thick disk in models with low orbital inclination angles of mergers are also in
good agreement with the latest observational results. Our Galactic chemical
evolution models can explain both the observed metallicity distribution
functions (MDFs) and correlations between [Mg/Fe] and [Fe/H] for the two disks
in a self-consistent manner.
