The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-489)

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 489 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体模拟套件的相关结果。本次Cosmogrid模拟在边长为30兆秒差距（Mpc）的立方盒中开展，共包含2048³个粒子。单个粒子的质量为1.28×10^5太阳质量（Msun），该分辨率足以分辨超暗矮星系。我们发现，晕质量函数与谢斯-托尔曼（Sheth & Tormen）拟合函数在低至约10^7太阳质量的范围内均保持良好一致性。我们对三个质量最大的星系群尺度晕结构开展了球对称平均密度剖面分析，这三个晕的尺度对应星系群级别，且各自包含至少1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率相较于-1更为平缓。我们还发现晕集中度与晕质量存在显著相关性。不过，集中度参数的质量依赖关系无法用单一幂律函数描述，但基于纳瓦罗等人（Navarro et al.）提出的普雷斯-谢克特（Press-Schechter）理论构建的简单模型，与该依赖关系吻合度较好。自旋参数与晕质量之间未发现显著相关性。对于质量大于约10^8太阳质量的晕结构，其集中度与自旋参数的概率分布函数均可通过对数正态分布得到良好拟合。次晕丰度随晕质量的变化而变化。星系尺度的晕结构相较于约10^11太阳质量的晕结构，其拥有的次晕数量多出50%。本数据集为2048³分辨率模拟集合的第489个快照。