Partitioning the Galactic halo with Gaussian Mixture Models
Partitioning the Galactic halo with Gaussian Mixture Models
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DOI：
10.1088/1674-4527/21/5/128
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发表时间：
2021-01
影响因子：
1.8
通讯作者：
Xilong Liang;Yuqin Chen;Jingkun Zhao;Gang Zhao
中科院分区：
文献类型：
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作者：
Xilong Liang;Yuqin Chen;Jingkun Zhao;Gang Zhao
银河系晕被认为是与附近的矮星系合并形成的。为了探测银河晕的不同组成部分，我们应用高斯混合模型方法，根据金属丰度、[Mg/Fe]比和空间速度（VR，V_（max））四个参数，对APOGEE DR 16星表中[Fe/H] < -0.7 dex的贫金属星进行了研究。通过分析它们在（[M/H]，[Mg/Fe]），（VR，V_r），（Zmax，偏心率），（能量，Lz）和（[Mg/Mn]，[Al/Fe]）坐标上的分布，确定了9个星系群，其中4个来自晕（第1，3，4，5群），1个来自厚盘（第6群），1个来自薄盘（第8群），1个来自矮星系（第7群）。其余两组分别由观测效应（第9组）和薄盘与厚盘之间的横截面分量（第2组）引起。研究发现，在极外层吸积晕（第1组）中，银河系中诞生的恒星无论是从化学上还是运动学上都无法与其他星系吸积的恒星区分开来。在金属丰度为−1.6 < [Fe/H] < -0.7 dex的中等金属丰度下，吸积晕主要由盖亚-土卫二-香肠亚结构（第5族）组成，在化学和运动学空间上都可以很容易地与第4族（原地晕族）区分开来。第4族的一些恒星可能来自盘面，而一些盘面恒星可以通过共振效应散射到高轨道，如Zmax与能量坐标所示。我们还显示了晕的主要成分的空间分布和吸积成分的比例没有显示出明确的银河系半径的关系。
The Galactic halo is supposed to form from merging with nearby dwarf galaxies. In order to probe different components of the Galactic halo, we have applied the Gaussian Mixture Models method to a selected sample of metal poor stars with [Fe/H] < –0.7 dex in the APOGEE DR16 catalogue based on four-parameters, metallicity, [Mg/Fe] ratio and spatial velocity (VR , Vϕ ). Nine groups are identified with four from the halo (group 1, 3, 4 and 5), one from the thick disk (group 6), one from the thin disk (group 8) and one from dwarf galaxies (group 7) by analyzing their distributions in the ([M/H], [Mg/Fe]), (VR , Vϕ ), (Zmax, eccentricity), (Energy, Lz) and ([Mg/Mn], [Al/Fe]) coordinates. The rest of the two groups are respectively caused by observational effect (group 9) and the cross section component (group 2) between the thin disk and the thick disk. It is found that in the extremely outer accreted halo (group 1), stars born in the Milky Way cannot be distinguished from those accreted from other galaxies either chemically or kinematically. In the intermediate metallicity of −1.6 < [Fe/H] < –0.7 dex, the accreted halo is mainly composed of the Gaia-Enceladus-Sausage substructure (group 5), which can be easily distinguished from group 4 (the in-situ halo group) in both chemical and kinematic space. Some stars of group 4 may come from the disk and some disk stars can be scattered to high orbits by resonant effects as shown in the Zmax versus Energy coordinate. We also displayed the spatial distribution of main components of the halo and the ratio of accreted components do not show clear relation to the Galactic radius.