The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-040)

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 040 of the 2048³ resolution collection.

本研究展示了基于标准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30百万秒差距（Mpc）的立方体计算框内开展，总粒子数达2048³。单个粒子质量为1.28×10^5倍太阳质量（M☉），该分辨率足以分辨超暗矮星系。研究表明，暗物质晕质量函数在低至~10^7 M☉的范围内，与Sheth-Tormen拟合公式吻合良好。我们分析了三个质量最大的星系群尺度暗物质晕的球对称平均密度剖面，这三个晕均包含至少1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率均比-1更为平缓。同时我们发现，暗物质晕的浓度参数与晕质量存在显著相关性。然而浓度参数的质量依赖关系无法用单一幂律描述，但基于Navarro等人提出的Press-Schechter理论的简化模型，能够与该依赖关系实现较好吻合。自旋参数则与晕质量未表现出显著相关性。对于质量大于~10^8 M☉的暗物质晕，其浓度和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。子晕丰度与晕质量相关。星系级暗物质晕的子晕数量比~10^11 M☉级晕多50%。本数据集为2048³分辨率模拟集合的第040号快照。