Early chemo-dynamical evolution of dwarf galaxies deduced from enrichment of r-process elements
Early chemo-dynamical evolution of dwarf galaxies deduced from enrichment of r-process elements
复制标题
DOI：
10.1093/mnras/stw3342
复制
发表时间：
2016-12
影响因子：
4.8
通讯作者：
Y. Hirai;Y. Ishimaru;T. Saitoh;M. Fujii;J. Hidaka;T. Kajino
中科院分区：
文献类型：
--
作者：
Y. Hirai;Y. Ishimaru;T. Saitoh;M. Fujii;J. Hidaka;T. Kajino
本星系群中极度贫金属（EMP）恒星的快速中子俘获过程（r过程元素）合成的丰富元素为我们阐明银河系晕的早期演化历史提供了线索。本星系群矮星系也会以类似的方式随着银河系晕的构建块而演化。然而，构建模块的化学动力学演化如何影响 r 过程元素的丰度尚不清楚。在本文中，我们使用具有不同动力学时间和总质量的矮星系模型进行了一系列模拟，这些模型决定了恒星形成的历史。我们发现，动力学时间超过 100 Myr 的星系的恒星形成率低于 $10^{-3} M_{\odot}$ yr$^{-1}$，并且在早期阶段缓慢地富集金属。这些星系可以解释在银河系晕 EMP 恒星中观察到的 r 过程丰度的大分散性，而不管它们的总质量如何。另一方面，第一次中子星合并出现在星系中较高的金属丰度，其动力学时间比典型的中子星合并时间短。 r过程元素的散射主要来自星际介质中金属的不均匀性，而$\alpha$元素的散射主要来自每个超新星的产量差异。我们的结果表明，未来对 EMP 恒星中 r 过程元素的观测将能够限制本星系群的早期化学动力学演化。
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.