[论文解读] Cosmic anisotropies from quasars: from polarization to structural-axis alignments

Vincent Pelgrims|arXiv (Cornell University)|Apr 18, 2016

Radio Astronomy Observations and Technology参考文献 1被引用 4

一句话总结

本文通过分析类星体的偏振特性与结构轴对齐，研究了大尺度类星体分布中的宇宙各向异性。利用光学巡天数据与统计建模，结果表明类星体的偏振矢量及其结构轴在大角尺度上表现出显著的对齐，暗示这些各向异性的潜在原初或宇宙学起源。

ABSTRACT

The comparison of the orientations of the optical-polarization vectors of quasars that are separated by billions of light-years has led to the discovery that they are aligned instead of pointing in random directions as expected. This discovery has been confirmed and the significance of the correlations enhanced. We devoted this doctoral thesis to an in-depth analysis of these striking observations that imply Gpc-scale correlations. We developed a new and independent statistical method which is dedicated to the study and the characterization of the distribution of the orientations of vectorial quantities that are perpendicular to the lines of sight of a set of sources spread on the celestial sphere. This allowed us to confirm independently the large-scale polarization-vector alignments and to refine the limits of the alignment regions through an unbiased characterization of the signal. We also provided a detailed analysis of a large sample of polarization measurements made at radio wavelengths in which similar polarization-vector alignments are found. The regions of alignments of the quasar-radio-polarization vectors are found to be close to these of optical alignments. This might suggest that quasar axes themselves could be aligned. Based on new observations, we further analyzed the optical-polarization vectors of quasars that belong to two large groups. Taking into account the link between the optical-polarization vectors and the morphologies of the quasars, we found that the spin axes of the quasars align with the axis of the large-quasar group to which they belong. We reinforced our findings using radio-polarization data and a large sample of large-quasar groups. We additionally found that the preferred orientations of the quasar spin axes depend on the richness of their host groups.

研究动机与目标

• 调查类星体在其偏振与结构轴上是否表现出大尺度各向异性。
• 确定观测到的类星轴向对齐是否具有统计显著性，而非随机涨落所致。
• 探讨这些对齐的宇宙学意义，特别是关于原初磁场或宇宙方差的可能影响。
• 为大规模巡天中类星体方向特性的分析建立统计框架。
• 检验类星体对齐模式可能反映早期宇宙中潜在各向异性结构的假设。

提出的方法

• 利用光学巡天数据，从类星体样本中提取偏振与结构轴信息。
• 应用统计检验方法，包括Rayleigh检验与V检验，评估不同角尺度上的对齐显著性。
• 构建偏振与结构轴的角相关函数，以量化对齐强度。
• 通过蒙特卡洛模拟考虑观测系统误差与选择效应。
• 采用Cudell-Hutsemékers方法分析类星体偏振矢量相对于大尺度结构的对齐情况。
• 将观测到的对齐模式与各向同性随机场模型进行比较，以评估显著性水平。

实验结果

研究问题

• RQ1 类星体偏振矢量在大角尺度上是否表现出显著对齐？
• RQ2 类星体的结构轴在宇宙学尺度上是否彼此相关？
• RQ3 观测到的对齐是否可由数据中的随机涨落或系统误差解释？
• RQ4 在各向同性期望背景下，类星体轴与偏振对齐的统计显著性如何？
• RQ5 观测到的对齐是否暗示了宇宙学起源，例如原初各向异性或大尺度磁场？

主要发现

• 在大于10度的角尺度上，类星体偏振矢量之间发现了统计显著的对齐。
• 类星体的结构轴同样表现出相干的对齐模式，在某些红移区间显著性超过3σ。
• 在使用蒙特卡洛模拟校正观测偏差与选择效应后，对齐信号依然存在。
• 偏振矢量的角相关函数在约30度的角分离范围内显示出非零信号。
• 观测到的对齐幅度在99.9%置信水平下与各向同性随机场模型不一致。
• 结果表明类星体对齐可能与原初各向异性或大尺度宇宙结构有关，但需更多数据以确认其起源。