The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-157)

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 157 of the 2048³ resolution collection.

我们展示了基于一致性冷暗物质（LCDM）模型的“宇宙网格（Cosmogrid）”宇宙学N体（N-body）模拟套件的研究结果。该模拟在边长为30百万秒差距（Mpc）的立方体计算盒中完成，共包含2048³个粒子，单个粒子质量为1.28×10^5倍太阳质量（Msun），足以分辨超暗矮星系（ultra-faint dwarfs）。我们发现，暗物质晕（halo）质量函数与希思-托门（Sheth & Tormen）拟合公式在低至约10^7倍太阳质量的范围内均保持良好一致性。我们对三个质量最大的星系群尺度暗物质晕开展了球对称平均密度剖面分析，这三个晕至少包含1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率变得比-1更为平缓。我们还发现暗物质晕的浓度参数与晕质量存在显著相关性。尽管浓度参数的质量依赖关系无法用单一幂律描述，但由纳瓦罗等人基于普雷斯-谢克特（Press-Schechter）理论提出的简单模型与该依赖关系吻合良好。自旋参数与暗物质晕质量并无相关性。对于质量大于约10^8倍太阳质量的暗物质晕，其浓度参数与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。次晕（subhalo）丰度与暗物质晕质量相关：星系尺度的暗物质晕所含次晕数量比约10^11倍太阳质量的暗物质晕多50%。本数据集为2048³分辨率模拟集中的第157个快照。