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Neutron star mergers are one of the candidate astrophysical site(s) of r-process. Several chemical evolution studies however pointed out that the observed abundance of r-process is difficult to reproduce by neutron star mergers. In this study, we aim to clarify the enrichment of r-process elements in the Local Group dwarf galaxies. We carry out numerical simulations of galactic chemo-dynamical evolution using an N-body/smoothed particle hydrodynamics code, ASURA. We construct a chemo-dynamical evolution model for dwarf galaxies assuming that neutron star mergers are the major source of r-process elements. Our models reproduce the observed dispersion in [Eu/Fe] as a function of [Fe/H] with neutron star mergers with a merger time of 100 Myr. We find that star formation efficiency and metal mixing processes during the first ≲ 300 Myr of galaxy evolution are important to reproduce the observations. This study supports that neutron star mergers are a major site of r-process.
Observed large scatters in abundances of neutron-capture elements in metal-poor stars may suggest incomplete mixing of the interstellar medium at the beginning of the Galaxy. Comparing predictions by an inhomogeneous chemical evolution model and new observational results with Subaru HDS, we attempt to constrain the origins of r-process elements.
While the origin of r-process nuclei remains a long-standing mystery, recent spectroscopic studies of extremely metal-poor stars in the Galactic halo strongly suggest that it is associated with core-collapse supernovae. In addition, recent comprehensive analysis of such stars implies the presence of the “weak” r-process that is responsible for only lighter nuclei with A <130. In this study, we show that the weak r-process nuclei can be produced in the neutrino winds from a typical proto-neutron star of $1.4 M_\odot$. This suggests that the significant fraction of weak r-process elements (Sr, Y, Zr, etc.) originate from typical core-collapse supernovae with the progenitor mass range of ∼ 10–$20 M_\odot$
We study the roles of type Ia (SNIa) and type II supernovae (SNII) in enrichment of the intra-cluster medium (ICM). Considering stellar [Fe/H] of ellipticals, iron mass in ICM to luminosity ratios, and [α/Fe] of ICM, we show that ~ 53% of iron in ICM comes from SNIa. While clusters keep all of ejecta from ellipticals, we obtain the observational evidence for that groups of galaxies lose parts of the gas by supernovae-driven winds. This ‘group wind’ scenario is confirmed by an 1D hydrodynamical model.
Combining X-ray data for clusters of galaxies, groups, and elliptical galaxies, we have obtained the evidence for that groups eject parts of the intra-group medium (IGM) via supernovae-driven ‘group winds’ like ellipticals. This scenario is confirmed by 1D hydrodynamical simulations.
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