Early chemo-dynamical evolution of dwarf galaxies deduced from
  enrichment of r-process elements
  The abundance of elements synthesized by the rapid neutron-capture process
(r-process elements) of extremely metal-poor (EMP) stars in the Local Group
galaxies gives us clues to clarify the early evolutionary history of the Milky
Way halo. The Local Group dwarf galaxies would have similarly evolved with
building blocks of the Milky Way halo. However, how the chemo-dynamical
evolution of the building blocks affects the abundance of r-process elements is
not yet clear. In this paper, we perform a series of simulations using dwarf
galaxy models with various dynamical times and total mass, which determine
star-formation histories. We find that galaxies with dynamical times longer
than 100 Myr have star formation rates less than $10^{-3} M_{\odot}$ yr$^{-1}$
and slowly enrich metals in their early phase. These galaxies can explain the
observed large scatters of r-process abundance in EMP stars in the Milky Way
halo regardless of their total mass. On the other hand, the first neutron star
merger appears at a higher metallicity in galaxies with a dynamical time
shorter than typical neutron star merger times. The scatters of r-process
elements mainly come from inhomogeneity of the metals in the interstellar
medium whereas the scatters of $\alpha$-elements are mostly due to the
difference in the yield of each supernova. Our results demonstrate that the
future observations of r-process elements in EMP stars will be able to
constrain the early chemo-dynamical evolution of the Local Group galaxies.
