The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-602)

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 602 of the 2048³ resolution collection.

本研究展示了基于标准Λ冷暗物质（LCDM）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）的周期性立方体盒子中完成，总粒子数为2048³个，单个粒子质量为1.28×10^5倍太阳质量（Msun），该质量分辨率足以解析超暗矮星系。研究发现，晕质量函数在低至约10^7倍太阳质量的范围内，与Sheth-Tormen拟合函数具有良好的一致性。我们分析了三个处于星系群尺度的大质量晕的球平均密度剖面，这三个晕各自包含至少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更为平缓。我们还发现晕浓度与晕质量存在显著相关性，不过浓度参数的质量依赖关系无法通过单一幂律进行描述，而基于Navarro等人依托Press-Schechter理论提出的简单模型，则与该质量依赖关系吻合良好。自旋参数与晕质量之间未呈现出显著相关性。对于质量大于约10^8倍太阳质量的晕而言，浓度和自旋的概率分布函数均可通过对数正态分布得到良好拟合。次晕的丰度依赖于晕质量：星系尺度的晕所拥有的次晕数量，比约10^11倍太阳质量的晕多出50%。本数据集为2048³分辨率系列中的第602个快照。