The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-582)

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 582 of the 2048³ resolution collection.

本研究展示了基于一致性Λ冷暗物质（LCDM）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30百万秒差距的立方体盒子中开展，共包含2048³个粒子，单个粒子质量为1.28×10^5 Msun（太阳质量），该分辨率足以分辨超暗矮星系（ultra-faint dwarfs）结构。研究发现，晕质量函数（halo mass function）与Sheth-Tormen拟合函数（Sheth & Tormen fitting function）在低至~10^7 Msun的质量范围内均保持良好一致性。我们对三个处于星系群尺度（galaxy group size）的大质量晕开展了球平均密度轮廓（spherically averaged density profiles）分析，每个晕至少包含1.7亿个粒子；结果显示，在最内侧半径处，这些晕的密度轮廓斜率陡度小于-1。同时我们还发现，晕浓度参数（concentration parameter）与晕质量存在显著相关性，但该相关性无法用单一幂律函数描述；不过基于Navarro等人提出的Press-Schechter理论（Press-Schechter theory）构建的简化模型，可与该质量依赖关系实现合理吻合。自旋参数（spin parameter）与晕质量则未表现出明显相关性。对于质量大于~10^8 Msun的晕，其浓度参数与自旋参数的概率分布函数（probability distribution functions）均可通过对数正态分布（log-normal distribution）得到良好拟合。次晕丰度（subhalo abundance）依赖于晕质量：星系尺度的晕所拥有的次晕数量比质量约为10^11 Msun的晕多出50%。本数据集为2048³分辨率模拟集合中的第582号快照（snapshot）。