卫星星系的平面：当例外是规则时
Planes of satellite galaxies: when exceptions are the rule
摘要：
银河系（MW）和仙女座星系（M31）卫星系统内平面结构的探测已经被报道为与标准宇宙学模型（$Λ$ CDM）的预测完全矛盾。由于在定义平面构型时存在模糊性，因此不清楚如何解释$Λ$ CDM中MW和M31平面的低发生率。我们调查卫星飞机周围的星系质量晕的高分辨率宇宙学模拟确定的患病率。我们发现，平面结构是非常常见的，和10%的$Λ$ CDM晕有更突出的平面比那些存在于本地组。虽然卫星星系的平面无处不在，但它们的性质却有很大的差异。这排除了使用一个或两个系统作为宇宙学的小尺度探测器，因为需要大量的卫星系统样本来获得物体与物体之间变化的良好测量。这种差异被误解为本地组和$Λ$ CDM预测中观察到的卫星平面之间的差异。事实上，大约10%的$Λ$ CDM星系晕有卫星平面，它们和MW和M31平面一样罕见。在评估卫星平面的探测显著性时，“别处看”效应起着重要作用，考虑到这一点，MW和M31系统的显著性水平分别被高估了30和100倍。
英文摘要：
The detection of planar structures within the satellite systems of both the Milky Way (MW) and Andromeda (M31) has been reported as being in stark contradiction to the predictions of the standard cosmological model ($Λ$CDM). Given the ambiguity in defining a planar configuration, it is unclear how to interpret the low incidence of the MW and M31 planes in $Λ$CDM. We investigate the prevalence of satellite planes around galactic mass haloes identified in high resolution cosmological simulations. We find that planar structures are very common, and that ~10% of $Λ$CDM haloes have even more prominent planes than those present in the Local Group. While ubiquitous, the planes of satellite galaxies show a large diversity in their properties. This precludes using one or two systems as small scale probes of cosmology, since a large sample of satellite systems is needed to obtain a good measure of the object-to-object variation. This very diversity has been misinterpreted as a discrepancy between the satellite planes observed in the Local Group and $Λ$CDM predictions. In fact, ~10% of $Λ$CDM galactic haloes have planes of satellites that are as infrequent as the MW and M31 planes. The look-elsewhere effect plays an important role in assessing the detection significance of satellite planes and accounting for it leads to overestimating the significance level by a factor of 30 and 100 for the MW and M31 systems, respectively.
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