The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-616)

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 616 of the 2048³ resolution collection.

本研究呈现基于一致性Λ冷暗物质（LCDM）模型的“Cosmogrid”宇宙学N体模拟套件的结果。本次Cosmogrid模拟在边长为30 Mpc（百万秒差距）的立方盒中开展，总粒子数为2048³。单个粒子的质量为1.28×10^5 Msun（太阳质量），该分辨率足以解析超暗矮星系。研究发现，晕质量函数在低至约10^7 Msun（太阳质量）的范围内，与谢特-托门（Sheth & Tormen）拟合函数具有良好的一致性。我们分析了三个质量最大的星系群级暗物质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。这些密度剖面的斜率在最内侧半径处变得比-1更为平缓。我们还发现暗物质晕的浓度与晕质量存在显著相关性。浓度参数的质量依赖性无法通过单一幂律表述，但基于纳瓦罗等人（Navarro et al.）提出的普雷斯-谢克特（Press-Schechter）理论构建的简单模型，与该依赖性的吻合度较高。自旋参数与暗物质晕质量未表现出相关性。对于质量大于约10^8 Msun（太阳质量）的暗物质晕，其浓度和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。次晕丰度随暗物质晕质量发生变化。星系级暗物质晕所拥有的次晕数量比约10^11 Msun（太阳质量）的晕多出50%。本数据集为2048³分辨率模拟集合的第616个快照。