The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-504)

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 504 of the 2048³ resolution collection.

本研究展示了基于标准Λ冷暗物质（ΛCDM）模型的「Cosmogrid」宇宙学N体模拟套件的相关结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方盒中完成，共包含2048³个粒子。单个粒子的质量为1.28×10^5倍太阳质量（M☉），该分辨率足以解析超暗矮星系（ultra-faint dwarfs）。我们发现，暗晕质量函数与谢斯-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、处于星系群尺度的暗晕结构开展了球对称平均密度剖面分析，这三个暗晕的粒子数均不少于1.7亿。在最内侧半径处，这些密度剖面的斜率比-1更为平缓。我们还发现暗晕浓度与暗晕质量存在显著相关性。然而浓度参数的质量依赖性无法用单一幂律函数描述，不过由纳瓦罗等（Navarro et al.）提出的、基于普雷斯-谢赫特（Press-Schechter）理论的简单模型，与该依赖性具有合理的吻合度。自旋参数与暗晕质量未表现出明显相关性。对于质量大于约10^8倍太阳质量的暗晕结构，其浓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。次晕丰度与暗晕质量相关：星系级暗晕结构的次晕数量比约10^11倍太阳质量的暗晕结构多出50%。本数据集为2048³分辨率系列中的第504个快照（snapshot）。