The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-494)

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 494 of the 2048³ resolution collection.

我们展示了基于标准协和Lambda冷暗物质（LCDM）模型的"Cosmogrid"宇宙学N体（N-body）模拟套件的研究结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方计算盒中完成，共采用2048³个粒子完成计算。每个粒子的质量为1.28×10^5太阳质量（Msun），该分辨率足以解析超暗矮星系。我们发现，暗晕质量函数在低至约10^7太阳质量的范围内，与Sheth与Tormen提出的拟合函数吻合良好。我们对三个质量最大的星系群级暗晕的球对称平均密度轮廓展开了分析，这三个暗晕均包含至少1.7亿个粒子。这些密度轮廓在最内侧半径处的斜率缓于-1。我们还发现暗晕的浓度参数与质量之间存在显著的相关性。浓度参数的质量依赖性无法通过单一幂律函数描述，但基于Navarro等人提出的Press-Schechter理论构建的简单模型，与该依赖性表现出合理的吻合性。暗晕的自旋参数（spin parameter）与晕质量之间未表现出相关性。对于质量大于约10^8太阳质量的暗晕，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（log-normal distribution）得到良好拟合。子晕（subhalo）的丰度依赖于暗晕的质量。星系尺度的暗晕的子晕数量比约10^11太阳质量的暗晕多出50%。本数据集为2048³分辨率模拟集合中的第494个快照。