Age-dating Red Giant Stars Associated with Galactic Disk and Halo Substructures
Age-dating Red Giant Stars Associated with Galactic Disk and Halo Substructures
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DOI：
10.3847/1538-4357/ac0532
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发表时间：
2021-05
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影响因子：
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通讯作者：
S. Grunblatt;J. Zinn;A. Price-Whelan;R. Angus;Nicholas Saunders;M. Hon;A. Stokholm;E. Bellinger-E.-Belling
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文献类型：
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作者：
S. Grunblatt;J. Zinn;A. Price-Whelan;R. Angus;Nicholas Saunders;M. Hon;A. Stokholm;E. Bellinger-E.-Belling
银河系中绝大多数的晕星可能是由少量（约103）相对较大的矮星系吸积事件所吸积而成。然而，这些事件的时间是不好的约束，主要依赖于间接的动力学混合参数或不精确的年龄测量与碎片结构的恒星。在这里，我们的目标是推断出强大的恒星年龄与银河系的子结构，更直接地约束合并的历史银河系。通过结合运动学，asteroseismic和光谱数据，在可用的情况下，我们推断恒星年龄的样本10红巨星的运动学选择的恒星晕内，其中一个子集与盖亚-土卫二-香肠晕子结构，并比较他们的年龄在银河系盘3红巨星。尽管这里确定的绝对和相对年龄存在系统性差异，但该样本中恒星的年龄排名是稳健的。通过将相同的可观测输入传递到多个恒星年龄测定包，我们在我们的样本中测量了Gaia-Enceladus-Sausage恒星的加权平均年龄为8 ± 3（统计）。± 1（系统）Gyr.我们还使用等时线确定了盖亚-土卫二-香肠群的年龄等级，发现盖亚-土卫二-香肠群的年龄为8.0 −2.3+3.2 Gyr。虽然我们不能区分层次人口年龄的晕或磁盘结构与我们有限的数据和样本的恒星，这个框架应该允许一个独特的特征，银河系的子结构，使用更大的恒星样本和额外的数据在不久的将来。
The vast majority of Milky Way stellar halo stars were likely accreted from a small number (≲3) of relatively large dwarf galaxy accretion events. However, the timing of these events is poorly constrained and predominantly relies on indirect dynamical mixing arguments or imprecise age measurements of stars associated with debris structures. Here, we aim to infer robust stellar ages for stars associated with galactic substructures to more directly constrain the merger history of the Galaxy. By combining kinematic, asteroseismic, and spectroscopic data where available, we infer stellar ages for a sample of 10 red giant stars that were kinematically selected to be within the stellar halo, a subset of which are associated with the Gaia–Enceladus–Sausage halo substructure, and compare their ages to 3 red giant stars in the Galactic disk. Despite systematic differences in both absolute and relative ages determined here, age rankings of stars in this sample are robust. Passing the same observable inputs to multiple stellar age determination packages, we measure a weighted average age for the Gaia–Enceladus–Sausage stars in our sample of 8 ± 3 (stat.) ± 1 (sys.) Gyr. We also determine hierarchical ages using isochrones for the populations of Gaia–Enceladus–Sausage, in situ halo and disk stars, finding a Gaia–Enceladus–Sausage population age of 8.0 −2.3+3.2 Gyr. Although we cannot distinguish hierarchical population ages of halo or disk structures with our limited data and sample of stars, this framework should allow a distinct characterization of Galactic substructures using larger stellar samples and additional data available in the near future.