The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-430)

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 430 of the 2048³ resolution collection.

本研究展示基于标准ΛCDM（LCDM）宇宙学模型的“宇宙网格（Cosmogrid）”宇宙学N体模拟套件的结果。本次宇宙网格（Cosmogrid）模拟在边长为30百万秒差距（Mpc）的计算盒中完成，总粒子数达2048³个。每个粒子的质量为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，晕质量函数与希思-托门（Sheth & Tormen）拟合函数在低至约10^7倍太阳质量的范围内均保持良好一致性。我们分析了三个质量最大的晕的球对称平均密度剖面，这三个晕处于星系群尺度，且至少包含1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率变得比-1更为平缓。本研究还发现晕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用单一幂律描述，但基于纳瓦罗等人（Navarro et al.）提出的普雷斯-谢赫特（Press-Schechter）理论的简单模型，与该依赖关系具有合理的一致性。自旋参数与晕质量之间不存在相关性。对于质量大于约10^8倍太阳质量的晕，其集中度和自旋参数的概率分布函数均可通过对数正态分布得到良好拟合。子晕丰度与晕质量相关：星系尺度的晕所拥有的子晕数量比约10^11倍太阳质量的晕多50%。本数据集为2048³分辨率模拟集合的第430个快照。