The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-758)

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 758 of the 2048³ resolution collection.

我们展示了基于标准ΛCDM（Lambda Cold Dark Matter）模型的宇宙网格（Cosmogrid）宇宙学N体模拟套件的研究结果。本次Cosmogrid模拟在边长为30兆秒差距的立方盒中开展，共包含2048³个粒子，单个粒子质量为1.28×10^5 Msun（太阳质量），该分辨率足以分辨超暗矮星系。我们发现，晕质量函数在低至约10^7 Msun的范围内，与谢斯-托尔曼（Sheth & Tormen）拟合函数吻合良好。我们分析了三个处于星系群尺度的大质量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；其密度剖面的斜率在最内侧半径处变得比-1更平缓。我们还发现晕浓度与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描述，但基于纳瓦罗等人（Navarro et al.）提出的普雷斯-谢克特（Press-Schechter）理论的简单模型，与该依赖性的吻合度较高。自旋参数与晕质量未表现出相关性。对于质量大于约10^8 Msun的晕，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。亚晕丰度与晕质量相关：星系尺度的晕所拥有的亚晕数量比约10^11 Msun的晕多50%。本数据集为2048³分辨率模拟集合中的第758个快照。