四面体坍缩：同时形成暗物质晕、暗丝和暗壁的旋转玩具模型
Tetrahedral collapse: a rotational toy model of simultaneous dark-matter halo, filament and wall formation
摘要：
我们讨论了一个理想化的晕形成模型，其中一个崩溃的晕节点是四面体的，从它的四个面中的每一个突出的细丝，并与连接每对细丝的壁。在这个模型中，细丝在形成时通常是旋转的，当且仅当细丝中有一些旋转时，晕才会旋转。这是“折纸近似”中最简单的可能的全三维晕塌缩，其中空隙是无旋的，并且形成暗物质结构的暗物质片被允许在位置-速度相空间中折叠，但不拉伸（即，其密度不能沿溪流变化）。在整体尺度上，四个暗条方向，以及其他三个量，如暗条自旋，足以确定坍缩的所有性质：晕的形状、质量和自旋;每单位长度的密度和所有暗条的自旋;以及每单位面积的壁的质量。如果细丝是正四面体排列的，细丝的性质遵循简单的定律，让人想起角动量守恒。该模型可能是最有用的在理解相邻星系之间的自旋相关性加入细丝;这些相关性将给出星系之间的内在排列，理解精确的宇宙学弱透镜测量至关重要。
英文摘要：
We discuss an idealized model of halo formation, in which a collapsing halo node is tetrahedral, with a filament extruding from each of its four faces, and with a wall connecting each pair of filaments. In the model, filaments generally spin when they form, and the halo spins if and only if there is some rotation in filaments. This is the simplest-possible fully three-dimensional halo collapse in the 'origami approximation,' in which voids are irrotational, and the dark-matter sheet out of which dark-matter structures form is allowed to fold in position-velocity phase space, but not stretch (i.e., it cannot vary in density along a stream). Up to an overall scaling, the four filament directions, and only three other quantities, such as filament spins, suffice to determine all of the collapse's properties: the shape, mass, and spin of the halo; the densities per unit length and spins of all filaments; and masses per unit area of the walls. If the filaments are arranged regular-tetrahedrally, filament properties obey simple laws, reminiscent of angular-momentum conservation. The model may be most useful in understanding spin correlations between neighboring galaxies joined by filaments; these correlations would give intrinsic alignments between galaxies, essential to understand for accurate cosmological weak-lensing measurements.
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