The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-029)

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 029 of the 2048³ resolution collection.

本研究展示了基于标准Λ冷暗物质（ΛCDM）一致性模型的“Cosmogrid”宇宙学N体模拟套件的结果。该模拟在边长为30百万秒差距（Mpc）的周期性盒子中开展，总粒子数为2048³，单个粒子质量为1.28×10^5倍太阳质量（Msun），该分辨率足以分辨超暗矮星系。研究发现，晕质量函数与谢尔思-托尔曼（Sheth & Tormen）拟合公式在低至约10^7 Msun的质量范围内均保持良好一致性。我们分析了三个星系群级别的最大质量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缓于-1。此外，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关系无法用单一幂律函数描述，但基于纳瓦罗（Navarro）等人提出的普雷斯-谢赫特（Press-Schechter）理论构建的简单模型，与该依赖关系的吻合度较高。自旋参数与晕质量未表现出显著相关性。对于质量大于约10^8 Msun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（log-normal distribution）得到良好拟合。次晕的丰度依赖于宿主晕质量：星系级晕的次晕数量比约10^11 Msun的晕多出50%。本数据集为2048³分辨率模拟集合的第029号快照。