御夫座圆盘的教训：寻找银河系的异位圆盘尚未结束
Lessons from the Auriga discs: The hunt for the Milky Way's ex-situ disc is not yet over
摘要：
我们的特点的贡献，吸积材料的御夫座项目，一套高分辨率的磁流体动力学宇宙学模拟晚型星系的移动网格代码AREPO的星系盘。我们的目标是探索银河系圆盘中是否有一个重要的吸积（或异位）恒星成分隐藏在近圆形轨道人口中，这是由原位出生的恒星所主导的。我们的模型的三分之一显示出显着的异位光盘，但这部分会更大，如果限制轨道圆度放松。大部分非原位物质（$\gtrsim 50\%$）来自单个大质量卫星（$> 6 \times 10^{10}~M_{\odot}$）。这些卫星以各种各样的坠落时间和倾角（最大可达$85^{\circ}$）吸积。异位椎间盘比原位椎间盘更厚、更老、更贫金属。它们显示出一个平坦的中位年龄剖面，这与在原地成分中观察到的负梯度不同。因此，在近圆形轨道上的老恒星样本中识别出非原位圆盘的可能性朝着圆盘的外围增加。我们展示了三个例子，除了异位光盘，有一个强烈的旋转暗物质组件。有趣的是，其中两个非原位恒星盘显示出与原位盘一致的轨道圆度分布。因此，它们在典型的运动学研究中不会被检测到。
英文摘要：
We characterize the contribution from accreted material to the galactic discs of the Auriga Project, a set of high resolution magnetohydrodynamic cosmological simulations of late-type galaxies performed with the moving-mesh code AREPO. Our goal is to explore whether a significant accreted (or ex-situ) stellar component in the Milky Way disc could be hidden within the near-circular orbit population, which is strongly dominated by stars born in-situ. One third of our models shows a significant ex-situ disc but this fraction would be larger if constraints on orbital circularity were relaxed. Most of the ex-situ material ($\gtrsim 50\%$) comes from single massive satellites ($> 6 \times 10^{10}~M_{\odot}$). These satellites are accreted with a wide range of infall times and inclination angles (up to $85^{\circ}$). Ex-situ discs are thicker, older and more metal-poor than their in-situ counterparts. They show a flat median age profile, which differs from the negative gradient observed in the in-situ component. As a result, the likelihood of identifying an ex-situ disc in samples of old stars on near-circular orbits increases towards the outskirts of the disc. We show three examples that, in addition to ex-situ discs, have a strongly rotating dark matter component. Interestingly, two of these ex-situ stellar discs show an orbital circularity distribution that is consistent with that of the in-situ disc. Thus, they would not be detected in typical kinematic studies.
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