探索千禧年模拟中的非线性密度场。概率分布函数
Exploring the non-linear density field in the Millennium simulations with tessellations - I. The probability distribution function
摘要：
我们使用Delaunay Tessellation Field Estimation（DTFE）来研究Millennium（MS）和Millennium-II（MS-II）模拟的单点密度分布函数。DTFE技术直接基于粒子位置，而不需要任何类型的平滑或分析网格，从而对通过模拟解决的所有非线性结构提供高灵敏度。为了确定一点密度概率分布函数（PDF）的形状的详细起源，我们根据其宿主FoF晕的质量分解模拟粒子，并检查不同晕质量范围对全局密度PDF的贡献。我们模型的一个点分布的FoF晕在每个晕质量箱与一组理想化的NFW暗物质晕的蒙特卡罗实现，发现这再现的测量从N体模拟相当不错，除了一个小的过剩存在于模拟结果。这种过剩随着晕圈质量的增加而增加。我们表明，它的起源在于子结构，这变得越来越丰富，更好地解决了更大规模的暗物质晕。我们证明了在质量较小的晕中，一点分布函数的高密度尾部受到引力软化长度和质量分辨率的严重影响。特别是，我们发现这两个参数是更重要的密度PDF比模拟量的准确测量。结合我们的结果，从个人晕质量箱，我们发现，一个点的密度PDF的一部分，起源于崩溃的晕，但可以很好地描述了一个简单的叠加一组NFW晕与预期的宇宙学丰度在解决的质量范围。然而，过渡区的低密度未结合的材料是没有很好地捕捉到这样的分析晕模型。
英文摘要：
We use the Delaunay Tessellation Field Estimator (DTFE) to study the one-point density distribution functions of the Millennium (MS) and Millennium-II (MS-II) simulations. The DTFE technique is based directly on the particle positions, without requiring any type of smoothing or analysis grid, thereby providing high sensitivity to all non-linear structures resolved by the simulations. In order to identify the detailed origin of the shape of the one-point density probability distribution function (PDF), we decompose the simulation particles according to the mass of their host FoF halos, and examine the contributions of different halo mass ranges to the global density PDF. We model the one-point distribution of the FoF halos in each halo mass bin with a set of Monte Carlo realizations of idealized NFW dark matter halos, finding that this reproduces the measurements from the N-body simulations reasonably well, except for a small excess present in simulation results. This excess increases with increasing halo mass. We show that its origin lies in substructure, which becomes progressively more abundant and better resolved in more massive dark matter halos. We demonstrate that the high density tail of the one-point distribution function in less massive halos is severely affected by the gravitational softening length and the mass resolution. In particular, we find these two parameters to be more important for an accurate measurement of the density PDF than the simulated volume. Combining our results from individual halo mass bins we find that the part of the one-point density PDF originating from collapsed halos can nevertheless be quite well described by a simple superposition of a set of NFW halos with the expected cosmological abundance over the resolved mass range. The transition region to the low-density unbound material is however not well captured by such an analytic halo model.
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