The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-026)

We present the results of the "Cosmogrid" cosmological N-body simulation suites based on the concordance LCDM model. The Cosmogrid simulation was performed in a 30 Mpc box with 2048³ particles. The mass of each particle is 1.28x10^5 Msun, which is sufficient to resolve ultra-faint dwarfs. We found that the halo mass function shows good agreement with the Sheth & Tormen fitting function down to ~10^7 Msun. We have analyzed the spherically averaged density profiles of the three most massive halos which are of galaxy group size and contain at least 170 million particles. The slopes of these density profiles become shallower than -1 at the inner most radius. We also find a clear correlation of halo concentration with mass. The mass dependence of the concentration parameter cannot be expressed by a single power law, however a simple model based on the Press-Schechter theory proposed by Navarro et al. gives reasonable agreement with this dependence. The spin parameter does not show a correlation with the halo mass. The probability distribution functions for both concentration and spin are well fitted by the log-normal distribution for halos with the masses larger than ~10^8 Msun. The subhalo abundance depends on the halo mass. Galaxy-sized halos have 50% more subhalos than ~10^11 Msun halos have. This is snapshot 026 of the 2048³ resolution collection.

我们展示了基于标准Λ冷暗物质（ΛCDM）模型的"Cosmogrid"宇宙学N体模拟套件的研究结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的计算盒子中开展，共包含2048³个粒子。每个粒子的质量为1.28×10^5倍太阳质量（Msun），足以分辨超暗矮星系。我们发现，暗晕（halo）质量函数与希思-托门（Sheth & Tormen）拟合函数在低至约10^7倍太阳质量的范围内均保持良好一致性。我们分析了三个质量最大的暗晕的球对称平均密度剖面，这三个暗晕的尺度对应星系群级别，且至少包含1.7亿个粒子。这些密度剖面在最内侧半径处的斜率相较于-1更为平缓。我们还发现暗晕集中度与质量之间存在显著的相关性。集中度参数的质量依赖关系无法用单一幂律描述，但基于纳瓦罗（Navarro）等人提出的普雷斯-谢赫特（Press-Schechter）理论的简单模型，与该依赖关系具有合理的一致性。自旋参数与暗晕质量并无显著相关性。对于质量大于约10^8倍太阳质量的暗晕，其集中度与自旋的概率分布函数均可通过对数正态分布得到良好拟合。子晕丰度随暗晕质量变化。星系级暗晕的子晕数量比约10^11倍太阳质量的暗晕多50%。本数据集为2048³分辨率系列中的第026号快照。