The R -process Alliance: Enrichment of r -process Elements in a Simulated Milky Way–like Galaxy

作者：Yutaka Hirai, Timothy C. Beers, Young Sun Lee, Shinya Wanajo, Ian U. Roederer, Masaomi Tanaka, Masashi Chiba, Takayuki R. Saitoh, Vinicius M. Placco, Terese T. Hansen, Rana Ezzeddine, Anna Frebel, Erika M. Holmbeck, Charli M. Sakari · 发表于：The Astrophysical Journal · 年份：2025 · DOI：10.3847/1538-4357/adf10a · 被引用次数：4 · 研究领域：Scientific Research and Discoveries、Gamma-ray bursts and supernovae、Stellar, planetary, and galactic studies

Abstract We study the formation of stars with varying amounts of heavy elements synthesized by the rapid neutron-capture process ( r -process) based on our detailed cosmological zoom-in simulation of a Milky Way–like galaxy with an N -body/smoothed particle hydrodynamics code, asura . Most stars with no overabundance in r -process elements, as well as the strongly r -process-enhanced (RPE) r -II stars ([Eu/Fe] > +0.7), are formed in dwarf galaxies accreted by the Milky Way within the 6 Gyr after the Big Bang. In contrast, over half of the moderately enhanced r -I stars (+0.3 < [Eu/Fe] ≤ +0.7) are formed in the main in situ disk after 6 Gyr. Our results suggest that the fraction of r -I and r -II stars formed in disrupted dwarf galaxies is larger the higher their [Eu/Fe] is. Accordingly, the most strongly enhanced r -III stars ([Eu/Fe] > +2.0) are formed in accreted components. These results suggest that non- r -process-enhanced stars and r -II stars are mainly formed in low-mass dwarf galaxies that hosted either none or a single neutron star merger, while the r -I stars tend to form in the well-mixed in situ disk. We compare our findings with high-resolution spectroscopic observations of RPE metal-poor stars in the halo and dwarf galaxies, including those collected by the R -Process Alliance. We conclude that observed [Eu/Fe] and [Eu/Mg] ratios can be employed in chemical tagging of the Milky Way’s accretion history.