Origin of highly r-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
Origin of highly r-process-enhanced stars in a cosmological zoom-in simulation of a Milky Way-like galaxy
复制标题
类似银河系的宇宙学放大模拟中高度r过程增强的恒星的起源
DOI：
10.1093/mnras/stac2489
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发表时间：
2022
影响因子：
4.8
通讯作者：
Makino Junichiro
中科院分区：
文献类型：
--
作者：
Hirai Yutaka;Beers Timothy C;Chiba Masashi;Aoki Wako;Shank Derek;Saitoh Takayuki R;Okamoto Takashi;Makino Junichiro
热过程增强(RPE)恒星提供了银河系(MW)组装历史和最重元素的核合成的化石记录。热过程联盟(RPA)和其他机构的观测已经证实，许多RPE恒星与化学动力学标记的群有关，这些群很可能来自中波聚积的矮星系。然而，我们不知道RPE星是如何形成的。在这里，我们给出了一个类微波星系的宇宙学放大模拟的结果，它具有丰富的过程，在时间和质量上都具有最高的分辨率。由于这一进展，与以前的模拟不同，我们发现最高RPE(r-II；[Eu/Fe]>；+0.7)恒星形成于低质量矮星系中，这些星系在[Fe/H]的R过程元素中得到了浓缩，而那些金属丰度较高的恒星则是在原位形成的局部增强的气团中，这些气团不一定是矮星系的成员。这一结果表明，低质量吸积矮星系是具有[Fe/H]的r-II星的主要形成地点。我们还发现，大多数低金属度的r-II恒星都表现出类似晕的运动学。与观测结果类似，在同一晕中形成的Somer-II恒星在[Fe/H]中的色散较低，而在[Eu/Fe]中的色散较大。模拟的R-II星的比例与RPA的观测结果相称，预测的光晕-II星的[Eu/Fe]分布与观测结果相符。这些结果表明，在矮小星系形成的早期阶段，RPE恒星可以作为矮小星系吸积的有价值的探测器。
Ther-process-enhanced (RPE) stars provide fossil records of the assembly history of the Milky Way (MW) and the nucleosynthesis of the heaviest elements. Observations by theR-Process Alliance (RPA) and others have confirmed that many RPE stars are associated with chemo-dynamically tagged groups, which likely came from accreted dwarf galaxies of the MW. However, we do not know how RPE stars are formed. Here, we present the result of a cosmological zoom-in simulation of an MW-like galaxy withr-process enrichment, performed with the highest resolution in both time and mass. Thanks to this advancement, unlike previous simulations, we find that most highly RPE (r-II; [Eu/Fe] > +0.7) stars are formed in low-mass dwarf galaxies that have been enriched inr-process elements for [Fe/H], while those with higher metallicity are formedin situ, in locally enhanced gas clumps that were not necessarily members of dwarf galaxies. This result suggests that low-mass accreted dwarf galaxies are the main formation site ofr-II stars with [Fe/H]. We also find that most low-metallicityr-II stars exhibit halo-like kinematics. Somer-II stars formed in the same halo show low dispersions in [Fe/H] and somewhat larger dispersions of [Eu/Fe], similar to the observations. The fraction of simulatedr-II stars is commensurate with observations from the RPA, and the distribution of the predicted [Eu/Fe] for halor-II stars matches that observed. These results demonstrate that RPE stars can be valuable probes of the accretion of dwarf galaxies in the early stages of their formation.