The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-523)

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 523 of the 2048³ resolution collection.

本研究呈现基于标准ΛCDM（LCDM）宇宙学模型的"Cosmogrid"宇宙学N体模拟（N-body simulation）套件的相关结果。本次Cosmogrid模拟在边长为30兆秒差距（Mpc）的立方计算盒中完成，共采用2048³个粒子，单个粒子质量为1.28×10^5太阳质量（Msun），该分辨率足以解析超暗矮星系。分析表明，暗物质晕（halo）质量函数在低至~10^7太阳质量的范围内与Sheth-Tormen拟合函数吻合良好。我们对三个星系群尺度的大质量暗物质晕开展了球对称平均密度剖面研究，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，研究发现暗物质晕浓度参数与晕质量存在显著相关性：该浓度参数的质量依赖关系无法通过单一幂律函数描述，但Navarro等人基于Press-Schechter理论提出的简化模型可与该依赖关系实现合理吻合。暗物质晕自旋参数则与晕质量无明显关联。对于质量大于~10^8太阳质量的暗物质晕，其浓度参数与自旋参数的概率分布函数均可通过对数正态分布进行良好拟合。次晕丰度依赖于暗物质晕质量：星系尺度的暗物质晕所拥有的次晕数量比~10^11太阳质量的暗物质晕多出50%。本数据集为2048³分辨率模拟集合中的第523号快照。