Observational evidence for a local underdensity in the Universe and its effect on the measurement of the Hubble constant
Observational evidence for a local underdensity in the Universe and its effect on the measurement of the Hubble constant
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DOI：
10.1051/0004-6361/201936400
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发表时间：
2019-07
影响因子：
6.5
通讯作者：
H. Boehringer;G. Chon;C. Collins
中科院分区：
文献类型：
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作者：
H. Boehringer;G. Chon;C. Collins
对于精确的宇宙学研究来说，了解我们观察宇宙的参考点的局部特性非常重要。特别是对于使用低红移距离指示器确定哈勃常数，观测到的值取决于所覆盖的距离范围内的平均物质密度。在这项研究中，我们使用星系团的空间分布来绘制当地宇宙中的物质密度分布。这项研究基于我们的 CLASSIX 星系团调查，该调查非常完整且特征明确，其中星系团是通过其 X 射线发射来检测的。总共有 1653 个位于“回避区”之外的星系团符合选择标准并参与了本研究。我们发现集群分布中的局部密度较低，约为 30-60%，向北延伸约 85 Mpc，向南延伸约 170 Mpc。我们详细研究了天空中几个区域的密度分布作为红移的函数。对于先前研究过星系密度分布的三个区域，我们发现星团和星系的密度分布之间有很好的一致性。校正簇分布中的偏差，我们推断在半径约为 100 (∼140) Mpc 的区域中，物质分布的密度较低，约为 -30 ± 15% (-20 ± 10%)。通过具有一致性宇宙学参数的 ΛCDM 宇宙中的结构形成理论计算找到这种低密度的概率，我们发现一个以 σ 值为 1.3 − 3.7 为特征的概率。这表明概率较低，但不确定性下限约为 10%，因此不能排除密度不足的存在。在这个低密度范围内，观测到的哈勃参数将大约 5.5 +2.1−2.8%，这解释了局部测量的 H0 值与普朗克宇宙微波背景各向异性观测推断出的哈勃参数值之间的部分差异。如果像许多现代分析那样包括局部低密度之外的距离指标，那么这种影响就会被削弱。
For precision cosmological studies it is important to know the local properties of the reference point from which we observe the Universe. Particularly for the determination of the Hubble constant with low-redshift distance indicators, the values observed depend on the average matter density within the distance range covered. In this study we used the spatial distribution of galaxy clusters to map the matter density distribution in the local Universe. The study is based on our CLASSIX galaxy cluster survey, which is highly complete and well characterised, where galaxy clusters are detected by their X-ray emission. In total, 1653 galaxy clusters outside the “zone of avoidance” fulfil the selection criteria and are involved in this study. We find a local underdensity in the cluster distribution of about 30–60% which extends about 85 Mpc to the north and ∼170 Mpc to the south. We study the density distribution as a function of redshift in detail in several regions in the sky. For three regions for which the galaxy density distribution has previously been studied, we find good agreement between the density distribution of clusters and galaxies. Correcting for the bias in the cluster distribution we infer an underdensity in the matter distribution of about −30 ± 15% (−20 ± 10%) in a region with a radius of about 100 (∼140) Mpc. Calculating the probability of finding such an underdensity through structure formation theory in a ΛCDM universe with concordance cosmological parameters, we find a probability characterised by σ-values of 1.3 − 3.7. This indicates low probabilities, but with values of around 10% at the lower uncertainty limit, the existence of an underdensity cannot be ruled out. Inside this underdensity, the observed Hubble parameter will be larger by about 5.5 +2.1−2.8%, which explains part of the discrepancy between the locally measured value of H0 compared to the value of the Hubble parameter inferred from the Planck observations of cosmic microwave background anisotropies. If distance indicators outside the local underdensity are included, as in many modern analyses, this effect is diluted.