在盖亚DR2的山脊、起伏和溪流上：相空间地形与N体棒的轨道结构的联系
On the ridges, undulations & streams in Gaia DR2: Linking the topography of phase-space to the orbital structure of an N-body bar
摘要：
我们探讨了第二次盖亚观测数据所揭示的银河系盘相空间子结构的起源，如$V_ϕ$ - $r$平面的脊、$V_ϕ$ - $r$-$V_r$空间的起伏和$V_ϕ$ - $V_r$平面的流.我们使用无碰撞N体模拟与空间薄和厚光盘，随着轨道积分，研究轨道结构接近外林德布拉德共振（OLR）的酒吧。我们发现，一个突出的，长寿命的脊形成在$V_ϕ$ - $r$平面由于OLR的流在$V_ϕ$ - $V_r$平面和检查的封闭周期性和捕获的振动轨道负责这些功能。我们发现，轨道周围的$x_1(1)$家庭进行小的天平动优先发现在负$V_r$，产生一个“喇叭”状的功能，而轨道具有较大的天平动振幅，周围的$x_1(2)$和$x_1(1)$家庭被困，构成积极的$V_r$子结构，即赫拉克勒斯的功能。这种变化的轨道天平动振幅将转化为薄/厚盘星的变化比率，这可能对该平面上的金属丰度分布产生影响。我们发现，太阳被放置在靠近OLR的情况下，会导致$V_r$在$V_ϕ$ - $V_r$平面（即大力士与“号角”）中的强烈不对称性，并随后导致$V_ϕ$ - $r$ - $V_r$空间的起伏。我们还探讨了一个方案，其中太阳被放置在更接近的酒吧共转，并发现酒吧扰动$alone$不能引起这些功能。
英文摘要：
We explore the origin of phase-space substructures revealed by the second Gaia data release in the disc of the Milky Way, such as the ridges in the $V_ϕ$-$r$ plane, the undulations in the $V_ϕ$-$r$-$V_r$ space and the streams in the $V_ϕ$-$V_r$ plane. We use a collisionless N-body simulation with co-spatial thin and thick discs, along with orbit integration, to study the orbital structure close to the Outer Lindblad Resonance (OLR) of the bar. We find that a prominent, long-lived ridge is formed in the $V_ϕ$-$r$ plane due to the OLR which translates to streams in the $V_ϕ$-$V_r$ plane and examine which closed periodic and trapped librating orbits are responsible for these features. We find that orbits which carry out small librations around the $x_1(1)$ family are preferentially found at negative $V_r$, giving rise to a `horn'-like feature, while orbits with larger libration amplitudes, trapped around the $x_1(2)$ and $x_1(1)$ families, constitute the positive $V_r$ substructure, i.e. the Hercules-like feature. This changing libration amplitude of orbits will translate to a changing ratio of thin/thick disc stars, which could have implications on the metallicity distribution in this plane. We find that a scenario in which the Sun is placed close to the OLR gives rise to a strong asymmetry in $V_r$ in the $V_ϕ$-$V_r$ plane (i.e. Hercules vs. `the horn') and subsequently to undulations in the $V_ϕ$-$r$-$V_r$ space. We also explore a scenario in which the Sun is placed closer to the bar corotation and find that the bar perturbation $alone$ cannot give rise to the these features.
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