Saraswati：一个超大质量~ 200兆秒差距超星系团
Saraswati: An Extremely Massive ~ 200 Megaparsec Scale Supercluster
摘要：
在这里，我们报告了在SDSS的条纹82区域发现的一个极其巨大的超星系团（称为Saraswati）。这个超星系团是星系和星系团的主要集中地，形成了一个在红移$z \approx 0.3$处至少跨越200 Mpc的壁状结构。这个巨大的结构被星系细丝、星系团和直径为$\sim40 - 170$兆秒差距的大空洞所包围。萨拉斯瓦蒂星系团的平均密度差$δ$（相对于宇宙背景物质密度）为$\gtrsim 1.62$，超星系团的主体至少包括43个大质量星系团（平均$z = 0.28$），总质量为$\sim 2 \times 10^{16} M_{\odot}$。球形坍缩模型表明半径为Mpc、质量至少为$ 4 \times 10^{15} M_{\odot}$的中心区域可能发生坍缩。这使它成为已知的少数几个最大和最大质量的超星系团之一，可与附近宇宙中最大质量的“沙普利集中”（$z \approx 0.046$）相媲美。萨拉斯瓦蒂超星系团及其周围地区揭示了一些极端大规模的，突出的物质密度增强在过去形成了$\sim4$ Gy，当时暗能量刚刚开始主导结构的形成。这个星系的浓度揭示了暗能量和宇宙学初始条件在超星系团形成中的作用，并测试了相互竞争的宇宙学模型。
英文摘要：
Here we report the discovery of an extremely massive and large supercluster (called Saraswati) found in the Stripe 82 region of SDSS. This supercluster is a major concentration of galaxies and galaxy clusters, forming a wall-like structure spanning at least 200 Mpc across at the redshift $z \approx 0.3$. This enormous structure is surrounded by a network of galaxy filaments, clusters, and large, $\sim40 - 170$ Mpc diameter, voids. The mean density contrast $δ$ (relative to the background matter density of the universe) of Saraswati is $\gtrsim 1.62$ and the main body of the supercluster comprises at least 43 massive galaxy clusters (mean $z = 0.28$) with a total mass of $\sim 2 \times 10^{16} M_{\odot}$. The spherical collapse model suggests that the central region of radius $\sim20$ Mpc and mass at least $ 4 \times 10^{15} M_{\odot}$ may be collapsing. This places it among the few largest and most massive superclusters known, comparable to the most massive `Shapley Concentration' ($z \approx 0.046$) in the nearby universe. The Saraswati supercluster and its environs reveal that some extreme large-scale, prominent matter density enhancements had formed $\sim4$ Gy in the past when dark energy had just started to dominate structure formation. This galactic concentration sheds light on the role of dark energy and cosmological initial conditions in supercluster formation, and tests the competing cosmological models.
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