The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-186)

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 186 of the 2048³ resolution collection.

我们展示了基于标准ΛCDM（LCDM）宇宙学模型的「Cosmogrid」宇宙学N体模拟套件的相关结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方盒中开展，共包含2048³个粒子。单个粒子的质量为1.28×10^5倍太阳质量（Msun），该分辨率足以分辨超暗矮星系（ultra-faint dwarfs）。我们发现，晕质量函数（halo mass function）与Sheth-Tormen拟合公式吻合良好，该吻合度可延伸至约10^7 Msun的尺度。我们针对三个质量最大的、处于星系群尺度（galaxy group size）的晕开展了球对称平均密度剖面（spherically averaged density profiles）分析，单晕粒子数均不少于1.7亿。在最内侧半径处，这些密度剖面的斜率相较于-1更为平缓。我们还发现晕浓度（halo concentration）与晕质量存在显著相关性。然而浓度参数随质量的依赖关系无法用单一幂律（power law）描述，不过基于Navarro等人提出的、以普雷斯-谢赫特理论（Press-Schechter theory）为基础的简单模型，能够与该依赖关系较好吻合。自旋参数（spin parameter）与晕质量之间不存在明显相关性。对于质量大于约10^8 Msun的晕而言，其浓度与自旋参数的概率分布函数（probability distribution functions）均能通过对数正态分布（log-normal distribution）得到良好拟合。次晕（subhalo）丰度与晕质量相关：星系量级的晕所拥有的次晕数量，比约10^11 Msun的晕多出50%。本数据集为2048³分辨率模拟集的第186个快照（snapshot）。