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arXiv 0910.3833astro-ph.CO
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描述星系分布的大尺度不均匀性

Characterizing the large scale inhomogeneity of the galaxy distribution

Francesco Sylos Labini

摘要:

为了研究星系结构是否与标准LCDM宇宙学的预测相一致,我们在这里着重分析了星系密度场的几个简单而基本的统计性质。也就是说,我们测试是否,在足够大的规模(即,r>10 Mpc/h),这是自平均的、均匀的,并且由波动的高斯概率密度函数表征。这是LCDM宇宙学的三个不同而清晰的预测,它们在代表该模型的宇宙学N体模拟产生的模拟星系目录中得到了实现。我们考虑一些简单的统计测量能够在有限样本中测试这些属性。我们讨论了对2度场星系红移巡天和斯隆数字巡天的几个样本的分析表明,星系结构在~100 Mpc/h尺度上是非自平均和不均匀的,因此与LCDM模型的预测有本质的不同。相应地,波动的概率密度函数显示出“厚尾”,因此它不同于高斯预测。最后,我们讨论了其他最近的观测结果,这些观测结果与LCDM的预测是不一致的,至少在理论上,它们与星系分布的高度不均匀性是相容的。我们指出,非均匀结构可以与统计各向同性和均匀性完全相容,从而与放松版本的宇宙学原理相容。

英文摘要:

In order to investigate whether galaxy structures are compatible with the predictions of the standard LCDM cosmology, we focus here on the analysis of several simple and basic statistical properties of the galaxy density field. Namely, we test whether, on large enough scales (i.e., r>10 Mpc/h), this is self-averaging, uniform and characterized by a Gaussian probability density function of fluctuations. These are three different and clear predictions of the LCDM cosmology which are fulfilled in mock galaxy catalogs generated from cosmological N-body simulations representing this model. We consider some simple statistical measurements able to tests these properties in a finite sample. We discuss that the analysis of several samples of the Two Degree Field Galaxy Redshift Survey and of the Sloan Digital Sky Survey show that galaxy structures are non self-averaging and inhomogeneous on scales of ~100 Mpc/h, and are thus intrinsically different from LCDM model predictions. Correspondingly the probability density function of fluctuations shows a "fat tail" and it is thus different from the Gaussian prediction. Finally we discuss other recent observations which are odds with LCDM predictions and which are, at least theoretically, compatible with the highly inhomogeneous nature of galaxy distribution. We point out that inhomogeneous structures can be fully compatible with statistical isotropy and homogeneity, and thus with a relaxed version of the Cosmological Principle.

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