The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-097)

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 097 of the 2048³ resolution collection.

本研究呈现基于标准Λ冷暗物质（ΛCDM）宇宙学模型的"Cosmogrid"宇宙学N体模拟套件的相关结果。该模拟在边长为30兆秒差距的计算盒中开展，共包含2048³个粒子，单个粒子质量为1.28×10^5 太阳质量（Msun），该分辨率足以分辨超暗矮星系（ultra-faint dwarfs）。研究发现，晕质量函数在低至~10^7 太阳质量的范围内与Sheth-Tormen拟合公式（Sheth & Tormen fitting function）吻合良好。我们对三个星系群尺度的大质量晕的球平均密度剖面进行了分析，每个晕至少包含1.7亿个粒子；结果显示，这些晕的密度剖面斜率在最内侧半径处变得比-1更为平缓。此外，我们还发现晕浓度（halo concentration）与质量存在显著相关性，但浓度参数的质量依赖关系无法用单一幂律函数描述；Navarro等人提出的基于Press-Schechter理论（Press-Schechter theory）的简化模型，能够较好地复现这一依赖关系。自旋参数（spin parameter）与晕质量未呈现显著相关性。对于质量大于~10^8 太阳质量的晕，其浓度和自旋的概率分布函数均可通过对数正态分布（log-normal distribution）得到良好拟合。次晕丰度与晕质量相关：星系尺度的晕所拥有的次晕数量比~10^11 太阳质量的晕多出50%。本数据集属于2048³分辨率模拟集的第097号快照。