The R-Process Alliance: Enrichment of R-process Elements in Simulated Milky Way-like Galaxies

The R-Process Alliance (RPA) has largely increased the number of measured stars with heavy elements synthesized by the rapid neutron-capture process (r-process). The next step of RPA is to understand the enrichment of r-process elements in the Milky Way using a large set of observed and simulated data. In this talk, I will review simulation studies on the enrichment of r-process elements. We study the formation of stars with varying amounts of r-process elements with our detailed cosmological zoom-in simulation of a Milky Way-like galaxy. Most stars with no overabundance in r-process elements, as well as the strongly r-process enhanced 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. We compare our findings with high-resolution spectroscopic observations of r-process-enhanced metal-poor stars in the halo and dwarf galaxies, including those collected by the RPA. We conclude that observed [Eu/Fe] and [Eu/Mg] ratios can be employed in chemical tagging of the Milky Way's accretion history.