The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-190)

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 190 of the 2048³ resolution collection.

我们展示了基于一致性Λ冷暗物质（ΛCDM）模型的"Cosmogrid"宇宙学N体模拟套件的结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方体模拟箱中完成，共包含2048³个粒子。单个粒子的质量为1.28×10^5倍太阳质量（Msun），足以分辨超暗矮星系（ultra-faint dwarfs）。我们发现，晕质量函数（halo mass function）与Sheth-Tormen拟合函数（Sheth & Tormen fitting function）在低至约10^7倍太阳质量的范围内均保持良好的一致性。我们对三个质量最大的晕的球对称平均密度剖面（spherically averaged density profiles）展开了分析，这三个晕处于星系群尺度，且至少包含1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率较-1更为平缓。我们还发现晕浓度参数（halo concentration）与晕质量存在显著的相关性。浓度参数的质量依赖关系无法用单一幂律描述，但基于Navarro等人（Navarro et al.）提出的Press-Schechter理论（Press-Schechter theory）的简单模型，能够与该依赖关系实现合理匹配。自旋参数（spin parameter）与晕质量之间不存在相关性。对于质量大于约10^8倍太阳质量的晕，其浓度参数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）实现良好拟合。次晕丰度（subhalo abundance）与晕质量相关：星系尺度的晕所拥有的次晕数量，比约10^11倍太阳质量的晕多50%。本数据集属于2048³分辨率模拟系列的第190个模拟快照（snapshot 190）。