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arXiv 1602.08541astro-ph.CO
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宇宙时间上宇宙学模拟中的空洞

Voids in cosmological simulations over cosmic time

Radosław Wojtak, Devon Powell, Tom Abel

摘要:

我们研究宇宙学模拟中的空洞演化,使用一种新的方法来跟踪空洞在宇宙时间。该方法是基于跟踪流域盆地(密度最小值周围的连续区域)发达的空隙在低红移,在一个规则的网格密度场。它使我们能够构建一个强大的和连续的映射之间的空隙在不同的红移,从初始条件到现在的时间。我们讨论了新的方法如何消除强大的虚假影响的数值起源时,空洞的演变是由连续的快照之间的匹配空洞(类比晕合并树)。我们应用新方法对标准LambdaCDM宇宙学模型进行了宇宙学模拟,研究了典型空洞(红移z=0时有效半径在6 Mpc/h ~ 20 Mpc/h之间)的体积、形状、物质密度分布和相对排列等基本性质的演化.在低红移的最终空隙似乎保留了初始条件下获得的配置的重要部分。空隙的数量以一种集体的方式演变,这几乎不改变轴比的总体分布。演化似乎有一个微弱的影响相互对齐的空隙,这意味着目前的状态是在很大程度上成立的原始密度场。我们提出的演化的暗物质密度分布计算等密度面符合实际形状的空隙。与球形密度分布不同,这种方法使我们能够证明理论上预测的桶状形状的最终密度分布的发展,表明一个宽平的核心和急剧过渡到高密度的空隙壁。

英文摘要:

We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids evolution is traced by matching voids between successive snapshots (by analogy to halo merger trees). We apply the new method to a cosmological simulation of a standard LambdaCDM cosmological model and study evolution of basic properties of typical voids (with effective radii between 6Mpc/h and 20Mpc/h at redshift z=0) such as volumes, shapes, matter density distributions and relative alignments. The final voids at low redshifts appear to retain a significant part of the configuration acquired in initial conditions. Shapes of voids evolve in a collective way which barely modifies the overall distribution of the axial ratios. The evolution appears to have a weak impact on mutual alignments of voids implying that the present state is in large part set up by the primordial density field. We present evolution of dark matter density profiles computed on iso-density surfaces which comply with the actual shapes of voids. Unlike spherical density profiles, this approach enables us to demonstrate development of theoretically predicted bucket-like shape of the final density profiles indicating a wide flat core and a sharp transition to high-density void walls.

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