扩展的ROSAT-ESO通量限制X射线星系团巡天（REFLEX II）V.探索南天的局部低密度
The extended ROSAT-ESO Flux-Limited X-ray Galaxy Cluster Survey (REFLEX II) V. Exploring a local underdensity in the Southern Sky
摘要：
根据对超新星和星系密度分布的观测，已经有几种说法认为我们位于宇宙的局部密度不足的区域。最近两项关于K波段星系巡天的研究为星系分布在200 - 300 Mpc距离的局部密度不足提供了新的支持。如果得到证实，如此大的局部欠密度将对解释宇宙学参数的局部测量产生重要影响。星系团已被证明是追踪宇宙大尺度结构的理想探针。本文利用REFLEX II星系团巡天中的X射线探测到的星系团，研究了南天的局域密度分布。从星系团的标准化同动数密度中，我们发现在南河外天区，在z ~0.04（~170 Mpc）的红移范围内，平均欠密度约为30 - 40%，显著性大于3.4 σ。在从300 Mpc到超过1 Gpc的更大尺度上，密度分布显得非常均匀。局部的低密度似乎是由南银河帽区域主导的。最近的一项研究将星系团的分布与K波段的星系分布进行了比较，结果表明星系和星系团在密度上非常接近。在南银河帽区域，两次调查都发现在红移范围z= 0到0.05的局部密度不足，而在南半球的北银河帽没有明显的密度不足。我们的结果不支持宇宙学模型，试图解释宇宙加速的一个大的局部空隙，因为我们发现的局部欠密度不是各向同性的，并限制在一个尺寸显着小于300 Mpc半径。
英文摘要：
Several claims have been made that we are located in a locally underdense region of the Universe based on observations of supernovae and galaxy density distributions. Two recent studies of K-band galaxy surveys have provided new support for a local underdensity in the galaxy distribution out to distances of 200 - 300 Mpc. If confirmed, such large local underdensities would have important implications on the interpretation of local measurements of cosmological parameters. Galaxy clusters have been shown to be ideal probes to trace the large-scale structure of the Universe. In this paper we study the local density distribution in the southern sky with the X-ray detected galaxy clusters from the REFLEX II cluster survey. From the normalized comoving number density of clusters we find an average underdensity of ~30 - 40% in the redshift range out to z ~0.04 (~170 Mpc) in the southern extragalactic sky with a significance larger than 3.4sigma. On larger scales from 300 Mpc to over 1 Gpc the density distribution appears remarkably homogeneous. The local underdensity seems to be dominated by the South Galactic Cap region. A comparison of the cluster distribution with that of galaxies in the K-band from a recent study shows that galaxies and clusters trace each other very closely in density. In the South Galactic Cap region both surveys find a local underdensity in the redshift range z= 0 to 0.05 and no significant underdensity in the North Galactic Cap at southern latitudes. Our results to not support cosmological models that attempt to interpret the cosmic acceleration by a large local void, since the local underdensity we find is not isotropic and limited to a size significantly smaller than 300 Mpc radius.
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