偶极子排斥器
The Dipole Repeller
摘要：
在宇宙学的标准（LCDM）模型中，宇宙已经从早期的均匀和各向同性阶段出现。结构的形成与密度不规则性和特殊速度的增长有关。我们的本星系群相对于宇宙微波背景（CMB）以631+/-20 km s-1的速度运动，并参与了一个延伸到至少20，000 km s-1距离的整体流。自从宇宙微波背景辐射偶极被发现以来，人们一直认为星系丰度的增加会导致星系的本星系群运动。然而，低密度区域的推动力与高密度区域的吸引力一样多，但它们缺乏光线，因此难以绘制图表。十年前有人提出，大约15，000 km s-1外的北半球密度不足是当地气流的重要因素。在这里，我们报告的运动学证据，这样一个欠密度。我们使用Wiener滤波器从Cosmicflows-2特有速度数据集重建大规模3D速度场，并识别主导局部动力学的吸引子和排斥子。我们在这里表明，当地的流动是由一个单一的吸引子-与沙普利浓度-和一个单一的先前身份不明的排斥。局部流的多极展开进一步支持了吸引子和排斥子的存在和作用。整体流（即偶极矩）在16，000 +/-4，500 km s-1的距离处与排斥极紧密（反）对齐。剪切张量（四极矩）的展开本征向量与Shapley吸引子在7，000 km s-1范围内紧密对齐。局部整体流与排斥器的紧密对齐进一步支持了其在塑造局部流中的主导作用。这个偶极子推斥器被预测与星系分布中的空洞有关。
英文摘要：
In the standard (LCDM) model of cosmology the universe has emerged out of an early homogeneous and isotropic phase. Structure formation is associated with the growth of density irregularities and peculiar velocities. Our Local Group is moving with respect to the cosmic microwave background (CMB) with a velocity 631+/-20 km s-1 and participates in a bulk flow that extends out to distances of at least 20,000 km s-1. Since the discovery of the CMB dipole, the implicit assumption was that excesses in the abundance of galaxies induce the Local Group motion. Yet, underdense regions push as much as overdensities attract but they are deficient of light and consequently difficult to chart. It was suggested a decade ago that an underdensity in the northern hemisphere roughly 15,000 km s-1 away is a significant actor in the local flow. Here we report on kinematic evidence for such an underdensity. We map the large scale 3D velocity field using a Wiener filter reconstruction from the Cosmicflows-2 dataset of peculiar velocities, and identify the attractors and repellers that dominate the local dynamics. We show here that the local flow is dominated by a single attractor -associated with the Shapley Concentration- and a single previously unidentified repeller. Multipole expansion of the local flow provides further support for the existence and role played by the attractor and repeller. The bulk flow (i.e. dipole moment) is closely (anti)aligned with the repeller at a distance of 16,000+/-4,500 km s-1. The expansion eigenvector of the shear tensor (quadrupole moment) is closely aligned with the Shapley Attractor out to 7,000 km s-1. The close alignment of the local bulk flow with the repeller provides further support for its dominant role in shaping the local flow. This Dipole Repeller is predicted to be associated with a void in the distribution of galaxies.
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