The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-763)

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 763 of the 2048³ resolution collection.

本工作展示了基于标准Λ冷暗物质（LCDM）模型的Cosmogrid宇宙学N体模拟套件的研究结果。该Cosmogrid模拟在边长为30兆秒差距（Mpc）的立方体计算盒中完成，总粒子数为2048³。单个粒子质量为1.28×10^5太阳质量（Msun），该分辨率足以分辨超暗矮星系（ultra-faint dwarfs）。研究发现，晕质量函数与Sheth-Tormen拟合函数（Sheth & Tormen fitting function）在低至约10^7 Msun（太阳质量）的范围内均保持良好一致性。我们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轮廓分析，这三个晕的尺度对应星系群级别，且各自包含至少1.7亿个粒子。在最内侧半径处，这些密度轮廓的斜率均浅于-1。同时我们还发现，晕的集中度与质量存在显著相关性。集中度参数的质量依赖性无法用单一幂律函数描述，但基于Navarro等人提出的Press-Schechter理论（Press-Schechter theory）构建的简单模型，与该依赖性的吻合度较高。自旋参数（spin parameter）与晕质量并无相关性。对于质量大于约10^8 Msun（太阳质量）的晕结构，其集中度与自旋的概率分布函数均可通过对数正态分布实现良好拟合。亚晕（subhalo）丰度与晕质量存在依赖关系：星系级别的晕结构所拥有的亚晕数量，比质量约为10^11 Msun（太阳质量）的晕多出50%。本数据为2048³分辨率模拟集的第763个快照（snapshot）。