The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-527)

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 527 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（N-body simulation）套件的研究结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方计算盒中开展，共采用2048³个粒子，单个粒子质量为1.28×10^5 太阳质量（Msun），该质量分辨率足以解析超暗矮星系。研究发现，晕质量函数（halo mass function）与Sheth-Tormen拟合公式（Sheth & Tormen fitting function）在低至约10^7 Msun的质量区间内均保持良好一致性。我们对三个处于星系群尺度的大质量晕开展了球平均密度轮廓（spherically averaged density profiles）分析，这些晕均包含至少1.7亿个粒子，其密度轮廓的斜率在最内侧半径处变得比-1更为平缓。我们同时发现，晕浓度与质量存在显著相关关系。浓度参数的质量依赖性无法通过单一幂律函数描述，但基于Navarro等人提出的Press-Schechter理论（Press-Schechter theory）构建的简单模型，与该依赖性的拟合结果较为合理。自旋参数与晕质量未表现出明显相关性。对于质量大于约10^8 Msun的晕，其浓度与自旋参数的概率分布函数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）与晕质量密切相关：星系尺度晕的次晕数量比约10^11 Msun的晕多50%。本数据集为2048³分辨率模拟系列的第527号快照（snapshot）。