The power of coordinate transformations in dynamical interpretations of Galactic structure
The power of coordinate transformations in dynamical interpretations of Galactic structure
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DOI：
10.1093/mnras/staa1987
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发表时间：
2020-06
影响因子：
4.8
通讯作者：
Jason A. S. Hunt;K. Johnston;A. Pettitt;E. Cunningham;D. Kawata;D. Hogg
中科院分区：
文献类型：
--
作者：
Jason A. S. Hunt;K. Johnston;A. Pettitt;E. Cunningham;D. Kawata;D. Hogg
$Gaia$DR 2提供了关于我们银河系中恒星位置和运动的前所未有的丰富信息，并突出了圆盘中的不平衡程度。当我们在更广泛的圆盘区域收集数据时，开始分析恒星的行为和角度变得越来越有吸引力，这些行为和角度专门标记轨道空间，而不是它们当前的相空间位置。从概念上讲，虽然$\bar{x}$和$\bar{v}$告诉我们潜在的和局部的相互作用，但在行动中，分组将具有相似频率的恒星放在一起，因此对发生在几个轨道上的动力学效应有相似的反应。引力作用和角度进一步细化了这一点，以隔离在太空中一起旅行的恒星，从而共享历史。混合使用这些坐标系统会混淆解释。例如，有人提出，通过将恒星移动到它们的引导半径，银河系的螺旋结构在$Gaia$ data \citep{Khoperskov+19 b}中可以看到脊状的超密度。然而，在这项工作中，我们表明，这些功能实际上是已知的运动学移动群，无论是在$L_z-\phi$和$v_{\mathrm{R}}-v_{\phi}$平面。通过模拟，我们展示了当我们转向银河系的全局视图时，这种区别将变得更加重要。作为一个例子，我们表明，径向速度波在银河系盘中看到的盖亚$和APOGEE应变得更强的作用角框架，它可以复制的瞬态螺旋结构。
$Gaia$ DR2 has provided an unprecedented wealth of information about the positions and motions of stars in our Galaxy, and has highlighted the degree of disequilibria in the disc. As we collect data over a wider area of the disc it becomes increasingly appealing to start analysing stellar actions and angles, which specifically label orbit space, instead of their current phase space location. Conceptually, while $\bar{x}$ and $\bar{v}$ tell us about the potential and local interactions, grouping in action puts together stars that have similar frequencies and hence similar responses to dynamical effects occurring over several orbits. Grouping in actions and angles refines this further to isolate stars which are travelling together through space and hence have shared histories. Mixing these coordinate systems can confuse the interpretation. For example, it has been suggested that by moving stars to their guiding radius, the Milky Way spiral structure is visible as ridge-like overdensities in the $Gaia$ data \citep{Khoperskov+19b}. However, in this work, we show that these features are in fact the known kinematic moving groups, both in the $L_z-\phi$ and the $v_{\mathrm{R}}-v_{\phi}$ planes. Using simulations we show how this distinction will become even more important as we move to a global view of the Milky Way. As an example, we show that the radial velocity wave seen in the Galactic disc in $Gaia$ and APOGEE should become stronger in the action-angle frame, and that it can be reproduced by transient spiral structure.