宇宙学码的比较：热气体和Shock Waves在大尺度结构中的性质
A Comparison of Cosmological Codes: Properties of Thermal Gas and Shock Waves in Large Scale Structures
摘要：
[...]我们目前的统计结果的热气体和冲击波性质的大体积模拟与三个不同的宇宙学数值代码：欧拉总变差递减代码TVD，欧拉分段抛物方法为基础的代码ENZO，和拉格朗日光滑粒子流体动力学代码GADGET。从一组共享的初始条件开始，我们提出了收敛测试的宇宙体积的边长100 Mpc/h，详细研究的热气体的形态和统计特性的质量和空间分辨率的函数在所有的代码。通过将冲击发现方法应用于每个代码，我们测量了冲击波的统计数据和相关的宇宙射线加速效率，在模拟样本和不同方法的结果中。我们讨论了制度的不确定性和分歧的代码，特别侧重于结果的尺度上的星系团。即使大部分的热和冲击性能是合理的协议之间的三个代码，但存在一些显着的差异（特别是欧拉方法和光滑粒子流体力学）。我们特别报告：（1）网格方法和SPH方法在模拟的最稀薄区域的平均气体密度、温度、熵、马赫数和激波热能通量的数值上存在巨大的差异（10-100）：（2）网格方法模拟的团簇内部存在熵核的暗示; d）网格方法和SPH方法在吸积激波形态上的相当大的差异。
英文摘要：
[...] We present results for the statistics of thermal gas and the shock wave properties for a large volume simulated with three different cosmological numerical codes: the Eulerian total variations diminishing code TVD, the Eulerian piecewise parabolic method-based code ENZO, and the Lagrangian smoothed-particle hydrodynamics code GADGET. Starting from a shared set of initial conditions, we present convergence tests for a cosmological volume of side-length 100 Mpc/h, studying in detail the morphological and statistical properties of the thermal gas as a function of mass and spatial resolution in all codes. By applying shock finding methods to each code, we measure the statistics of shock waves and the related cosmic ray acceleration efficiencies, within the sample of simulations and for the results of the different approaches. We discuss the regimes of uncertainties and disagreement among codes, with a particular focus on the results at the scale of galaxy clusters. Even if the bulk of thermal and shock properties are reasonably in agreement among the three codes, yet some significant differences exist (especially between Eulerian methods and smoothed particle hydrodynamics). In particular, we report: a) differences of huge factors (10-100) in the values of average gas density, temperature, entropy, Mach number and shock thermal energy flux in the most rarefied regions of the simulations between grid and SPH methods; b) the hint of an entropy core inside clusters simulated in grid codes; c) significantly different phase diagrams of shocked cells in grid codes compared to SPH; d) sizable differences in the morphologies of accretion shocks between grid and SPH methods.
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