标题： 高速下的次结构 I：在存在运动学次结构的情况下推断逃逸速度 显示英文标题

标题： Substructure at High Speed I: Inferring the Escape Velocity in the Presence of Kinematic Substructure

摘要： 局部逃逸速度为银河系的质量分布提供了有价值的输入，并需要理解恒星速度分布的尾部。按照 Leonard$\&$Tremaine (1990)，此后各种研究将恒星速度分布的尾部建模为$\propto (v_{\rm{esc}} -v)^k$，其中$v_{\rm{esc}}$是逃逸速度，$k$是分布的斜率。然而，在这些研究中，这两个参数被发现很大程度上是退化的，并且通常会对$k$施加一个狭窄的先验以限制$v_{\rm{esc}}$。此外，在存在多个运动学子结构的情况下，幂律形式的有效性可能会失效。在本文中，我们引入了一种策略，这是首次考虑运动学子结构的存在。我们将速度分布的尾部建模为多个幂律的和，而不需要施加强先验。使用模拟数据，我们展示了该方法在存在类似于最近发现的 Gaia Sausage 的运动学结构时的鲁棒性。在一篇配套论文中，我们利用 Gaia DR2 数据提出了逃逸速度的新测量结果，并随后得出了银河系的质量。 显示英文摘要

摘要： The local escape velocity provides valuable inputs to the mass profile of the Galaxy, and requires understanding the tail of the stellar speed distribution. Following Leonard $\&$ Tremaine (1990), various works have since modeled the tail of the stellar speed distribution as $\propto (v_{\rm{esc}} -v)^k$, where $v_{\rm{esc}}$ is the escape velocity, and $k$ is the slope of the distribution. In such studies, however, these two parameters were found to be largely degenerate and often a narrow prior is imposed on $k$ in order to constrain $v_{\rm{esc}}$. Furthermore, the validity of the power law form is likely to break down in the presence of multiple kinematic substructures. In this paper, we introduce a strategy that for the first time takes into account the presence of kinematic substructure. We model the tail of the velocity distribution as a sum of multiple power laws without imposing strong priors. Using mock data, we show the robustness of this method in the presence of kinematic structure that is similar to the recently-discovered Gaia Sausage. In a companion paper, we present the new measurement of the escape velocity and subsequently the mass of the Milky Way using Gaia DR2 data.