The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-746)

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 746 of the 2048³ resolution collection.

我们展示了基于标准ΛCDM模型的“Cosmogrid”宇宙学N体模拟（N-body simulation）套件的结果。Cosmogrid模拟在30兆秒差距（Mpc）的立方体区域内进行，包含2048³个粒子。每个粒子的质量为1.28×10^5太阳质量（Msun），足以解析超暗矮星系。我们发现，暗晕质量函数（halo mass function）与Sheth & Tormen拟合函数在低至约10^7太阳质量的范围内具有良好的一致性。我们分析了三个质量最大的暗晕的球平均密度剖面（density profile），这些暗晕达到星系群尺度，且包含至少1.7亿个粒子。这些密度剖面的斜率在最内半径处小于-1，即更为平缓。我们还发现暗晕浓度与质量之间存在明显的相关性。浓度参数的质量依赖性无法用单一幂律表示，但基于Navarro等人提出的Press-Schechter理论的简单模型与这种依赖性具有合理的一致性。自旋参数（spin parameter）与暗晕质量之间未显示出相关性。对于质量大于约10^8太阳质量的暗晕，浓度和自旋的概率分布函数均能被对数正态分布（log-normal distribution）很好地拟合。子暗晕（subhalo）的丰度取决于暗晕质量。星系尺度的暗晕比约10^11太阳质量的暗晕多50%的子暗晕。这是2048³分辨率集合中的第746个快照。