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arXiv 2308.08092astro-ph.GA
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基于径向作用量共轭角探索外盘的非对称子结构

Exploring asymmetric substructures of the outer disk based on the conjugate angle of the radial action

Y. Xu, C. Liu, Z. Li, H. Tian, Sarah A. Bird, H. J. Newberg, S. Shao, L. C. Deng

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53pages, 35 figures, 4 Tables, ApJ accepted
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AI总结：

研究利用径向作用量共轭角分析 LAMOST K 巨星外盘子结构，发现相螺旋相关团块及麒麟座区域集中特征，并用试验粒子模拟将其归因于人马座矮星系近期经过的扰动。

摘要：

我们使用径向作用量的共轭角（$θ_R$）——轨道相位的最佳表征——来探索此前在 LAMOST K 巨星中揭示的“中平面、北支、南支”以及“麒麟座区域”盘结构（Xu et al. 2020）。前三类子结构由其三维运动学分布识别，已被证明是相空间螺旋的投影（由非平衡相位混合产生）。在本工作中，我们发现所有这些与相螺旋相关的子结构在共轭角相空间中均表现出高度聚集，表明共轭角空间中的团块化是持续、不完全相位混合的一个特征。我们没有在“麒麟座区域”发现位于其中的 $Z-V_Z$ 相螺旋，但确实在共轭角空间中轨道相位从远心点到引导半径的象限内发现了一个高度集中的子结构。共轭角空间中该团块的存在提供了一种互补方式，将“麒麟座区域”与对一次显著引力相互作用事件所引发扰动的直接响应联系起来。利用试验粒子模拟，我们表明这些特征类似于人马座矮椭球星系最近一次经过撞击所造成的扰动。

英文摘要：

We use the conjugate angle of radial action ($θ_R$), the best representation of the orbital phase, to explore the "mid-plane, north branch, south branch" and "Monoceros area" disk structures that were previously revealed in the LAMOST K giants (Xu et al. 2020). The former three substructures, identified by their 3D kinematical distributions, have been shown to be projections of the phase space spiral (resulting from nonequilibrium phase mixing). In this work, we find that all of these substructures associated with the phase spiral show high aggregation in conjugate angle phase space, indicating that the clumping in conjugate angle space is a feature of ongoing, incomplete phase mixing. We do not find the $Z-V_Z$ phase spiral located in the "Monoceros area", but we do find a very highly concentrated substructure in the quadrant of conjugate angle space with the orbital phase from the apocenter to the guiding radius. The existence of the clump in conjugate angle space provides a complementary way to connect the "Monoceros area" with the direct response to a perturbation from a significant gravitationally interactive event. Using test particle simulations, we show that these features are analogous to disturbances caused by the impact of the last passage of the Sagittarius dwarf spheroidal galaxy.

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