Identifying Sagittarius Stream Stars by Their APOGEE Chemical Abundance Signatures
Identifying Sagittarius Stream Stars by Their APOGEE Chemical Abundance Signatures
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DOI：
10.3847/1538-4357/aafdac
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发表时间：
2019-01
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通讯作者：
S. Hasselquist;J. Carlin;J. Holtzman;M. Shetrone;C. Hayes;K. Cunha;V. Smith;R. Beaton;J. Sobeck
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作者：
S. Hasselquist;J. Carlin;J. Holtzman;M. Shetrone;C. Hayes;K. Cunha;V. Smith;R. Beaton;J. Sobeck
SDSS-IV Apache Point Observatory Galactic Evolution Experiment（APOGEE）巡天提供了分布在银河系大部分地区的176，000颗红巨星的18种化学元素的精确化学丰度，并包括对人马座矮球状星系（Sgr）核心的观测。Sgr的APOGEE化学丰度模式表明，它在大多数化学元素中与MW在化学上不同。我们采用k-均值聚类算法，以六维化学空间定义的[（C+N）/Fe]，[O/Fe]，[Mg/Fe]，[Al/Fe]，[Mn/Fe]，和[Ni/Fe]，以确定62 MW的星APOGEE样本中具有Sgr的化学丰度。在62颗恒星中，有35颗的盖亚运动学和位置与Sgr流的N体模拟预测的一致，并且可能是在最后两次近心通过期间（<2 Gyr前）从Sgr剥离的恒星。62颗恒星中的另外20颗表现出与Sgr流星难以区分的化学丰度，但处于高偏心轨道上，平均轨道半径为25 kpc。这些恒星很可能是“吸积”的晕群，被认为是8-11 Gyr前与MW单独合并的结果。我们还发现了一个超高速星星候选者。我们的结论是，Sgr在最近一次通过近心点之前富集到[Fe/H]<$-0.2。如果“吸积晕”是来自一次主要的吸积事件，那么这个祖先星系至少富集到[Fe/H] −0.6，并且在合并之前有着与Sgr相似的星星形成历史。
The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey provides precise chemical abundances of 18 chemical elements for ∼176,000 red giant stars distributed over much of the Milky Way Galaxy (MW), and includes observations of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). The APOGEE chemical abundance patterns of Sgr have revealed that it is chemically distinct from the MW in most chemical elements. We employ a k-means clustering algorithm to six-dimensional chemical space defined by [(C+N)/Fe], [O/Fe], [Mg/Fe], [Al/Fe], [Mn/Fe], and [Ni/Fe] to identify 62 MW stars in the APOGEE sample that have Sgr-like chemical abundances. Of the 62 stars, 35 have Gaia kinematics and positions consistent with those predicted by N-body simulations of the Sgr stream, and are likely stars that have been stripped from Sgr during the last two pericenter passages (<2 Gyr ago). Another 20 of the 62 stars exhibit chemical abundances indistinguishable from the Sgr stream stars, but are on highly eccentric orbits with median rapo ∼ 25 kpc. These stars are likely the “accreted” halo population thought to be the result of a separate merger with the MW 8–11 Gyr ago. We also find one hypervelocity star candidate. We conclude that Sgr was enriched to [Fe/H] ∼ −0.2 before its most recent pericenter passage. If the “accreted halo” population is from one major accretion event, then this progenitor galaxy was enriched to at least [Fe/H] ∼ −0.6, and had a similar star formation history to Sgr before merging.