The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-081)

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 081 of the 2048³ resolution collection.

本研究展示了基于标准Λ冷暗物质（LCDM）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）的计算盒子中完成，总粒子数为2048³。单个粒子质量为1.28×10^5倍太阳质量（Msun），该分辨率足以解析超暗矮星系。研究发现，晕质量函数与Sheth-Tormen拟合公式符合良好，拟合下限可达约10^7倍太阳质量。本研究分析了三个质量最大的星系群量级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较-1更为平缓（即斜率绝对值小于1）。本研究同时发现，晕的集中度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通过单一幂律函数表征，不过基于Press-Schechter理论、由Navarro等人提出的简化模型，与该依赖关系的吻合度较高。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倍太阳质量的晕，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很好地拟合。子晕的丰度与晕质量相关：星系量级的晕所拥有的子晕数量，比约10^11倍太阳质量的晕多出50%。本数据集为2048³分辨率模拟集合中的第081号快照。