The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-500)

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 500 of the 2048³ resolution collection.

本研究呈现基于标准Λ冷暗物质（LCDM）模型构建的"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）的立方体模拟盒中完成，共包含2048³个粒子，单个粒子质量达1.28×10^5倍太阳质量（M☉），该分辨率足以解析超暗矮星系。研究表明，晕质量函数在低至约10^7倍太阳质量的区间内，与Sheth & Tormen拟合函数吻合度极佳。我们针对三个质量最大的星系群级晕结构开展了球对称平均密度剖面分析，此类晕至少包含1.7亿个粒子；在最内侧半径处，这些密度剖面的斜率均缓于-1。同时发现晕浓度与质量存在显著相关关系，不过浓度参数的质量依赖关系无法通过单一幂律描述，而基于Navarro等人提出的Press-Schechter理论构建的简化模型，与该依赖关系的吻合度较高。自旋参数与晕质量则未表现出明显关联。对于质量大于约10^8倍太阳质量的晕结构，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实现良好拟合。次晕丰度随晕质量发生变化：星系级晕的次晕数量较约10^11倍太阳质量的晕多出50%。本数据集为2048³分辨率模拟集合的第500个快照。