和邻居住在一起。III。相互作用暗物质晕对自旋$-$轨道排列的研究
Living with Neighbors. III. Scrutinizing the Spin$-$Orbit Alignment of Interacting Dark Matter Halo Pairs
摘要：
我们提出了自旋$-$轨道对准（SOA;即，晕的自旋矢量和它的邻居的轨道角动量矢量之间的角度对准）提供了银河系角动量如何发展的重要线索。特别是，我们确定维里半径明智的接触晕对质量比从1/3到3的宇宙学$N$体模拟，并将它们分为合并和飞越子样本根据其总（动能+势能）的能量。在自旋$-$轨道角分布中，我们发现了一个显著的SOA，其中$75.0\pm0.6$ %的合并邻居和$58.7\pm0.6$ %的飞越邻居在轨道上。我们的样本的整体SOA主要是由快速旋转的晕驱动的，证实了良好对齐的相互作用使晕旋转得更快。更有趣的是，我们第一次发现了一个强大的数量过剩的近垂直，但仍然相互作用（$\sim75^{\circ}$）的自旋$-$轨道角分布的合并和飞越的情况下。这种非极性相互作用在缓慢旋转的晕中占主导地位，证明了错位的相互作用会降低晕的旋转。双极相互作用的频率与晕质量有关，而双极相互作用的频率与大尺度密度有关。这立即引发了自旋翻转现象，这是有条件的质量和环境。极间的相互作用很快就会翻转一个慢旋转体的自旋，使之与它邻居的轨道角动量一致。最后，我们提出了一个场景，连接SOA的周围大尺度结构的基础上自旋翻转参数。
英文摘要：
We present that the spin$-$orbit alignment (SOA; i.e., the angular alignment between the spin vector of a halo and the orbital angular momentum vector of its neighbor) provides an important clue to how galactic angular momenta develop. In particular, we identify virial-radius-wise contact halo pairs with mass ratios from 1/3 to 3 in a set of cosmological $N$-body simulations, and divide them into merger and flyby subsamples according to their total (kinetic+potential) energy. In the spin$-$orbit angle distribution, we find a significant SOA in that $75.0\pm0.6$ % of merging neighbors and $58.7\pm0.6$ % of flybying neighbors are on the prograde orbit. The overall SOA of our sample is mainly driven by fast-rotating halos, corroborating that a well-aligned interaction spins a halo faster. More interestingly, we find for the first time a strong number excess of nearly perpendicular but still prograde interactions ($\sim75^{\circ}$) in the spin$-$orbit angle distribution for both the merger and flyby cases. Such prograde-polar interactions predominate for slow-rotating halos, testifying that misaligned interactions reduce the halos' spin. The frequency of the prograde-polar interactions correlates with the halo mass, yet anticorrelates with the large-scale density. This instantly invokes the spin-flip phenomenon that is conditional on the mass and environment. The prograde-polar interaction will soon flip the spin of a slow-rotator to align with its neighbor's orbital angular momentum. Finally, we propose a scenario that connects the SOA to the ambient large-scale structure based on the spin-flip argument.
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