The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-150)

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 150 of the 2048³ resolution collection.

我们展示了基于标准Λ冷暗物质（LCDM）模型的Cosmogrid宇宙学N体模拟套件的相关结果。该Cosmogrid模拟在边长为30兆秒差距的立方体模拟盒子中完成，共包含2048³个粒子，单个粒子质量为1.28×10^5倍太阳质量，该分辨率足以分辨超暗矮星系。我们的分析显示，晕质量函数与希思-托门（Sheth & Tormen）拟合公式在低至~10^7倍太阳质量的范围内均保持良好一致性。我们针对三个质量最大的星系群尺度晕展开了球平均密度轮廓分析，这三个晕均包含至少1.7亿个粒子。在最内侧半径处，这些密度轮廓的斜率变得比-1更平缓。我们还发现晕集中度与质量之间存在显著相关性。集中度参数的质量依赖性无法用单一幂律函数描述，但由纳瓦罗等人（Navarro et al.）基于普雷斯-谢赫特（Press-Schechter）理论提出的简单模型，与该依赖性表现出合理的一致性。自旋参数与晕质量并未呈现出相关性。对于质量大于~10^8倍太阳质量的晕，其集中度与自旋的概率分布函数均可通过对数正态分布得到良好拟合。次晕丰度依赖于晕质量：星系尺度晕的次晕数量比质量约为10^11倍太阳质量的晕多50%。本数据集为2048³分辨率集合中的第150个快照。