孤立螺线对内禀自旋取向的探测
Detection of the Intrinsic Spin Alignments in Isolated Spiral Pairs
摘要：
本文给出了孤立螺旋星系对内禀星系排列的观测证据。从坦普尔等人在斯隆数字巡天数据第10版的通量限制星系样本中确定的星系群目录中，我们选择那些只由两个螺旋星系组成的星系群作为孤立的螺旋星系对，并调查它们的两个螺旋成员的自旋轴是否以及如何相互对齐。我们检测到一个明确的信号，内在的自旋对齐在孤立的螺旋对，这导致拒绝零假设在$99.9999\%$的置信水平，通过瑞利测试。研究还发现，由两个早型旋涡星系组成的孤立星系对表现出最强的内禀自旋对准信号，并且对准信号的强度取决于角间距以及成员星系的光度比。利用EAGLE流体动力学模拟中分辨出的仅由两个暗晕组成的暗物质晕，我们重复了同样的分析，但没有发现暗物质晕中恒星分量的自旋角动量矢量之间的任何对齐趋势，这与观测结果是矛盾的。一对夫妇可能的来源，这种明显的不一致的观测和数值结果进行了讨论。
英文摘要：
An observational evidence for the intrinsic galaxy alignments in isolated spiral pairs is presented. From the catalog of the galaxy groups identified by Tempel et al. in the flux limited galaxy sample of the Sloan Digital Sky Survey Data Release 10, we select those groups consisting only of two spiral galaxies as isolated spiral pairs and investigate if and how strongly the spin axes of their two spiral members are aligned with each other. We detect a clear signal of intrinsic spin alignment in the isolated spiral pairs, which leads to the rejection of the null hypothesis at the $99.9999\%$ confidence level via the Rayleigh test. It is also found that those isolated pairs comprising two early-type spiral galaxies exhibit the strongest signal of intrinsic spin alignment and that the strength of the alignment signal depends on the angular separation distance as well as on the luminosity ratio of the member galaxies. Using the dark matter halos consisting of only two subhalos resolved in the EAGLE hydrodynamic simulations, we repeat the same analysis but fail to find any alignment tendency between the spin angular momentum vectors of the stellar components of the subhalos, which is in tension with the observational result. A couple of possible sources of this apparent inconsistency between the observational and the numerical results are discussed.
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