The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (512-021)

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 021 of the 512³ resolution collection.

我们展示了基于标准Lambda冷暗物质模型（LCDM model）的"Cosmogrid"宇宙学N体模拟（N-body simulation）套件的结果。Cosmogrid模拟在一个30百万秒差距（Mpc）的盒子中进行，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）在低至~10^7太阳质量（Msun）时仍与Sheth & Tormen拟合函数高度一致。我们分析了三个质量最大的暗晕的球对称平均密度剖面（spherically averaged 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变得比-1更平缓。我们还发现暗晕浓度（halo concentration）与质量之间存在明显的相关性。浓度参数（concentration parameter）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（Press-Schechter theory）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）与暗晕质量之间没有相关性。对于质量大于~10^8太阳质量（Msun）的暗晕，其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。星系尺度暗晕的子暗晕数量比~10^11太阳质量（Msun）的暗晕多50%。这是512³分辨率集合中的第021号快照。