The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers
The COMBS Survey - II. Distinguishing the metal-poor bulge from the halo interlopers
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DOI：
10.1093/mnras/stab003
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发表时间：
2020-09
影响因子：
4.8
通讯作者：
M. Lucey;K. Hawkins;M. Ness;V. Debattista;A. Luna;M. Asplund;T. Bensby;L. Casagrande;S. Feltzing
中科院分区：
文献类型：
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作者：
M. Lucey;K. Hawkins;M. Ness;V. Debattista;A. Luna;M. Asplund;T. Bensby;L. Casagrande;S. Feltzing
摘要核球中的贫金属恒星是银河系形成历史的重要遗迹，模拟预测它们是银河系中最古老的恒星之一。为了确定它们是否真的是古老的恒星，我们必须了解它们的起源。目前，尚不清楚核球中的贫金属恒星（[Fe/H] l-1 dex）是否仅仅是晕的闯入者，一个独特的吸积种群，四四方方/花生状核球的一部分或经典的核球种群。在这项工作中，我们使用VLT/FLAMES摄谱仪的光谱来获得金属丰度估计，使用473颗凸起恒星的Ca-II三重态（其中187颗具有[Fe/H]l-1 dex），使用SkyMapper测光。我们还使用盖亚DR 2数据推断银河系的位置和速度沿着与523颗恒星的轨道特性。我们采用了概率轨道分析，发现我们的样本中约有一半的g 50%的概率被绑定到凸起，一半是晕闯入者。我们还看到，在我们的样品的整个范围内（~ 3 l [Fe/H] l 0.5），随着金属丰度的降低，晕圈闯入者的出现率稳步增加。我们的检查的运动学的限制相比，未绑定的恒星表明，金属贫凸起包括至少两个人口，那些局限于四四方方的/花生球和晕星通过内部星系。我们的结论是，轨道分析的方法，因为我们已经采用，是很重要的，以了解在内部区域的贫金属恒星的复合性质。
Abstract The metal-poor stars in the bulge are important relics of the Milky Way’s formation history, as simulations predict that they are some of the oldest stars in the Galaxy. In order to determine if they are truly ancient stars, we must understand their origins. Currently, it is unclear if the metal-poor stars in the bulge ([Fe/H] l -1 dex) are merely halo interlopers, a unique accreted population, part of the boxy/peanut-shaped bulge or a classical bulge population. In this work, we use spectra from the VLT/FLAMES spectrograph to obtain metallicity estimates using the Ca-II triplet of 473 bulge stars (187 of which have [Fe/H]l-1 dex), targeted using SkyMapper photometry. We also use Gaia DR2 data to infer the Galactic positions and velocities along with orbital properties for 523 stars. We employ a probabilistic orbit analysis and find that about half of our sample has a g 50% probability of being bound to the bulge, and half are halo interlopers. We also see that the occurrence rate of halo interlopers increases steadily with decreasing metallicity across the full range of our sample (-3 l [Fe/H] l 0.5). Our examination of the kinematics of the confined compared to the unbound stars indicates the metal-poor bulge comprises at least two populations; those confined to the boxy/peanut bulge and halo stars passing through the inner galaxy. We conclude that an orbital analysis approach, as we have employed, is important to understand the composite nature of the metal-poor stars in the inner region.