Early chemo-dynamical evolution of dwarf galaxies deduced from enrichment of r-process elements

TL;DR

This study uses simulations of dwarf galaxy evolution to understand how early chemo-dynamical processes influence r-process element enrichment in metal-poor stars, shedding light on the Milky Way's formation history.

Contribution

The paper introduces a simulation-based analysis linking dwarf galaxy dynamical times to r-process element abundance patterns in EMP stars, revealing the impact of early chemo-dynamical evolution.

Findings

Galaxies with longer dynamical times have slower metal enrichment.

Large r-process scatter in EMP stars can be explained by inhomogeneous metal distribution.

The timing of neutron star mergers depends on galaxy dynamical times.

Abstract

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.