The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-567)

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 567 of the 2048³ resolution collection.

我们展示了基于标准Λ冷暗物质（ΛCDM，Lambda Cold Dark Matter）模型的“Cosmogrid”宇宙学N体（N-body）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）的立方体计算盒中完成，共采用2048³个粒子。每个粒子的质量为1.28×10^5倍太阳质量（M☉），该分辨率足以解析超暗矮星系（ultra-faint dwarfs）。我们发现，晕质量函数在低至约10^7倍太阳质量的范围内，与Sheth-Tormen拟合公式吻合良好。我们分析了三个质量最大的星系群级晕的球对称平均密度剖面，这些晕的尺度对应星系群级别，且至少包含1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率变得比-1更平缓。我们还发现晕浓度与晕质量存在显著的相关性。不过浓度参数的质量依赖关系无法用单一幂律描述，但基于Navarro等人提出的普雷斯-谢赫特（Press-Schechter）理论的简单模型，与该依赖关系吻合较好。自旋参数与晕质量之间不存在相关性。对于质量大于约10^8倍太阳质量的晕，其浓度和自旋的概率分布函数均能通过对数正态分布（log-normal distribution）得到良好拟合。子晕的丰度依赖于晕质量。星系级晕的子晕数量比约10^11倍太阳质量的晕多50%。本数据集为2048³分辨率模拟套件的第567个模拟快照。