The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-684)

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 684 of the 2048³ resolution collection.

我们展示了基于标准Λ冷暗物质（ΛCDM）宇宙学模型的宇宙网格（Cosmogrid）宇宙学N体模拟套件的结果。该Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方体计算盒中完成，总粒子数达2048³。单个粒子质量为1.28×10^5倍太阳质量（M☉），足以分辨超暗矮星系（ultra-faint dwarfs）。我们发现，暗物质晕（halo）质量函数与希思-托门（Sheth & Tormen）拟合函数的吻合度极佳，匹配下限可达约10^7倍太阳质量。我们分析了三个质量最大的暗物质晕的球对称平均密度剖面：这些晕属于星系群（galaxy group）尺度，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会平缓至大于-1。我们还发现暗物质晕集中度（halo concentration）与晕质量存在显著相关性。集中度参数的质量依赖关系无法用单一幂律（power law）描述，但基于纳瓦罗（Navarro）等人提出的普雷斯-谢赫特（Press-Schechter）理论构建的简单模型，可与该依赖关系实现合理吻合。自旋参数（spin parameter）与暗物质晕质量不存在相关性。对于质量大于约10^8倍太阳质量的暗物质晕，其集中度与自旋参数的概率分布函数（probability distribution functions）均可通过对数正态分布（log-normal distribution）得到良好拟合。子晕丰度（subhalo abundance）与暗物质晕质量相关。星系尺度的暗物质晕所拥有的子晕数量比约10^11倍太阳质量的暗物质晕多出50%。本数据集为2048³分辨率系列中的第684号快照（snapshot）。