宇宙网的动力学分类
A Dynamical Classification of the Cosmic Web
摘要：
提出了宇宙网的动力学分类。大尺度环境被分为四种网络类型：空洞，片，丝和结。分类的基础上的变形张量，即Hessian的引力势，在一个网格上的评价。该分类基于对每个网格点处高于某个阈值lambda_th的本征值的数量进行计数，其中零个、一个、两个或三个这样的本征值的情况对应于空隙、片、细丝或结网格点。具有相同网属性的相邻网格点的集合（朋友的朋友）构成作为网对象的空隙、片、丝和结。一个简单的动力学考虑表明，λ_th应该近似为1，在适当的缩放变形张量。该算法已被应用和测试对一套（暗物质只）宇宙学N体模拟。特别是，体积和质量填充分数的依赖关系的lambda_th和分辨率已计算的四个网络类型。此外，还研究了孔隙和纤维的渗流特性。我们的主要发现是：（a）在lambda_th = 0.1时，所产生的网络分类再现了宇宙网络的视觉印象。(b)在0.2 < lambda_th < 0.4之间，一个由相互连接的细丝组成的网络与一个由相互连接的空隙组成的系统共存。这表明选择lambda_th作为定义宇宙网络的参数是合理的。(c)建议的分类的动力学性质提供了一个强大的框架，将环境信息纳入星系形成模型，特别是半分析的。
英文摘要：
A dynamical classification of the cosmic web is proposed. The large scale environment is classified into four web types: voids, sheets, filaments and knots. The classification is based on the evaluation of the deformation tensor, i.e. the Hessian of the gravitational potential, on a grid. The classification is based on counting the number of eigenvalues above a certain threshold, lambda_th at each grid point, where the case of zero, one, two or three such eigenvalues corresponds to void, sheet, filament or a knot grid point. The collection of neighboring grid points, friends-of-friends, of the same web attribute constitutes voids, sheets, filaments and knots as web objects. A simple dynamical consideration suggests that lambda_th should be approximately unity, upon an appropriate scaling of the deformation tensor. The algorithm has been applied and tested against a suite of (dark matter only) cosmological N-body simulations. In particular, the dependence of the volume and mass filling fractions on lambda_th and on the resolution has been calculated for the four web types. Also, the percolation properties of voids and filaments have been studied. Our main findings are: (a) Already at lambda_th = 0.1 the resulting web classification reproduces the visual impression of the cosmic web. (b) Between 0.2 < lambda_th < 0.4, a system of percolated voids coexists with a net of interconected filaments. This suggests a reasonable choice for lambda_th as the parameter that defines the cosmic web. (c) The dynamical nature of the suggested classification provides a robust framework for incorporating environmental information into galaxy formation models, and in particular the semi-analytical ones.
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