Implications of the Milky Way Travel Velocity for Dynamical Mass Estimates of the Local Group
Implications of the Milky Way Travel Velocity for Dynamical Mass Estimates of the Local Group
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DOI：
10.3847/1538-4357/aca01f
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发表时间：
2022-04
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影响因子：
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通讯作者：
Katherine Chamberlain;A. Price-Whelan;G. Besla;E. Cunningham;N. Garavito-Camargo;J. Peñarrubia;M. Petersen
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文献类型：
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作者：
Katherine Chamberlain;A. Price-Whelan;G. Besla;E. Cunningham;N. Garavito-Camargo;J. Peñarrubia;M. Petersen
本星系群（LG）的总质量是一个基本的量，可以解释其组成星系的轨道，并将LG置于宇宙学背景中。为数不多的几种可以直接推断总质量的方法之一是“计时论证”，它模拟了银河系（MW）和M31在平衡状态下的相对轨道。MW本身并不处于平衡状态，这是它合并历史的副产品，包括最近大麦哲伦云（LMC）的近心通过，最近的工作发现MW盘相对于外部恒星晕的“旅行速度”下限为1.32 km s−1。以前的定时参数测量试图解释这种非平衡状态，但仅限于对LMC影响的理论预测。在本文中，我们量化的旅行速度恢复LG质量估计使用几种不同的汇编最近的运动学测量M31的影响。我们发现，将测量值的旅行速度降低了10%-12%的推断LG质量相比，静态MW晕。用更远的示踪剂测量旅行速度可能会产生更大的值，这将进一步降低推断的LG质量。因此，新测得的旅行速度直接意味着较低的LG质量比从一个模型与静态MW晕，必须考虑在未来的动力学研究的本地体积。
The total mass of the Local Group (LG) is a fundamental quantity that enables interpreting the orbits of its constituent galaxies and placing the LG in a cosmological context. One of the few methods that allows inferring the total mass directly is the “Timing Argument,” which models the relative orbit of the Milky Way (MW) and M31 in equilibrium. The MW itself is not in equilibrium, a byproduct of its merger history and including the recent pericentric passage of the Large Magellanic Cloud (LMC), and recent work has found that the MW disk is moving with a lower bound “travel velocity” of ∼32 km s−1 with respect to the outer stellar halo. Previous Timing Argument measurements have attempted to account for this nonequilibrium state, but have been restricted to theoretical predictions for the impact of the LMC specifically. In this paper, we quantify the impact of a travel velocity on recovered LG mass estimates using several different compilations of recent kinematic measurements of M31. We find that incorporating the measured value of the travel velocity lowers the inferred LG mass by 10%–12% compared to a static MW halo. Measurements of the travel velocity with more distant tracers could yield even larger values, which would further decrease the inferred LG mass. Therefore, the newly measured travel velocity directly implies a lower LG mass than from a model with a static MW halo and must be considered in future dynamical studies of the Local Volume.