Orbital Torus Imaging: Using Element Abundances to Map Orbits and Mass in the Milky Way
Orbital Torus Imaging: Using Element Abundances to Map Orbits and Mass in the Milky Way
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DOI：
10.3847/1538-4357/abe1b7
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发表时间：
2020-11
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通讯作者：
A. Price-Whelan;D. Hogg;K. Johnston;M. Ness;H. Rix;R. Beaton;J. Brownstein;D. A. García-Hernández-D.-A.-García-H
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作者：
A. Price-Whelan;D. Hogg;K. Johnston;M. Ness;H. Rix;R. Beaton;J. Brownstein;D. A. García-Hernández-D.-A.-García-H
许多研究星系动力学的方法都假设引力势是简单的，分布函数是时不变的。在这些假设下，有传统的工具来推断恒星运动学观测的潜在参数（例如，牛仔裤模特）。然而，光谱巡天测量了许多恒星运动学之外的性质。在这里，我们提出了一种新的动力学推断方法，轨道环面成像，它利用运动学测量和元素丰度（或其他不变的标签）。我们利用的事实是，在稳定状态下，恒星的标签系统地变化与轨道特性（行动），但必须是不变的轨道相位（共轭角）。因此，相空间的轨道叶理必须与表面沿着重合，所有恒星标签分布的所有矩都是常数。经典统计学和贝叶斯方法都可以建立在此基础上;这些方法将更加稳健，比传统工具需要更少的假设，因为它们不需要（空间）调查选择函数的知识，也不涉及速度分布的二阶矩。我们执行一个经典的统计演示与红巨星分支星从APOGEE调查：我们在银河系盘的垂直轨道结构模型，以约束本地磁盘质量，规模的高度，和盘晕质量比（在固定的本地圆周速度）。我们发现，盘质量可以限制（天真地）在百分之几的水平与轨道环成像使用只有八个元素丰度比，展示了结合恒星标签与动力学不变量的承诺。
Many approaches to galaxy dynamics assume that the gravitational potential is simple and the distribution function is time invariant. Under these assumptions there are traditional tools for inferring potential parameters given observations of stellar kinematics (e.g., Jeans models). However, spectroscopic surveys measure many stellar properties beyond kinematics. Here we present a new approach for dynamical inference, Orbital Torus Imaging, which makes use of kinematic measurements and element abundances (or other invariant labels). We exploit the fact that, in steady state, stellar labels vary systematically with orbit characteristics (actions), yet must be invariant with respect to orbital phases (conjugate angles). The orbital foliation of phase space must therefore coincide with surfaces along which all moments of all stellar label distributions are constant. Both classical-statistics and Bayesian methods can be built on this; these methods will be more robust and require fewer assumptions than traditional tools because they require no knowledge of the (spatial) survey selection function and do not involve second moments of velocity distributions. We perform a classical-statistics demonstration with red giant branch stars from the APOGEE surveys: we model the vertical orbit structure in the Milky Way disk to constrain the local disk mass, scale height, and the disk–halo mass ratio (at fixed local circular velocity). We find that the disk mass can be constrained (naïvely) at the few-percent level with Orbital Torus Imaging using only eight element-abundance ratios, demonstrating the promise of combining stellar labels with dynamical invariants.