在噪声中看到模式：不违反均匀性的千兆秒差距尺度的“结构”
Seeing patterns in noise: Gigaparsec-scale `structures' that do not violate homogeneity
摘要：
Clowes等人（2013）最近报道了在斯隆数字巡天的DR 7类星体目录中发现了一个大型类星体群（LQG），被称为Huge-LQG，红移z~1.3。根据它的特征尺寸~500 Mpc和最长尺寸>1 Gpc，这种结构与大尺度均匀性和宇宙学原理不相容。如果这是真的，这将是对标准宇宙学模型的严重挑战。然而，均匀性尺度是一种平均性质，不一定受到单个大结构的发现的影响。我澄清了这一点，并提供了DR 7类星体目录的第一个分维分析，以证明它实际上是均匀的尺度以上，最多130 Mpc/h，这是远远低于上限的ΛCDM。此外，我表明，用于确定的巨大LQG算法定期发现更大的点群，扩展到Gpc尺度，在明确的均匀模拟的泊松点过程具有相同的密度的类星体目录。这提供了一个简单的零测试，适用于任何集群，从而发现在一个真正的目录，并建议，解释LQG作为“结构”是误导。
英文摘要：
Clowes et al. (2013) have recently reported the discovery of a Large Quasar Group (LQG), dubbed the Huge-LQG, at redshift z~1.3 in the DR7 quasar catalogue of the Sloan Digital Sky Survey. On the basis of its characteristic size ~500 Mpc and longest dimension >1 Gpc, it is claimed that this structure is incompatible with large-scale homogeneity and the cosmological principle. If true, this would represent a serious challenge to the standard cosmological model. However, the homogeneity scale is an average property which is not necessarily affected by the discovery of a single large structure. I clarify this point and provide the first fractal dimension analysis of the DR7 quasar catalogue to demonstrate that it is in fact homogeneous above scales of at most 130 Mpc/h, which is much less than the upper limit for ΛCDM. In addition, I show that the algorithm used to identify the Huge-LQG regularly finds even larger clusters of points, extending over Gpc scales, in explicitly homogeneous simulations of a Poisson point process with the same density as the quasar catalogue. This provides a simple null test to be applied to any cluster thus found in a real catalogue, and suggests that the interpretation of LQGs as `structures' is misleading.
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