The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-152)

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 152 of the 2048³ resolution collection.

本研究展示了基于一致性ΛCDM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（Mpc）的箱体中完成，共包含2048³个粒子，单个粒子质量为1.28×10^5倍太阳质量（Msun），该分辨率足以分辨超暗矮星系（ultra-faint dwarfs）。研究发现，暗物质晕（halo）质量函数与Sheth-Tormen拟合函数（Sheth & Tormen fitting function）在低至~10^7倍太阳质量的范围内均保持良好一致性。本研究分析了三个质量最大的暗物质晕的球对称平均密度剖面（spherically averaged density profiles）：这三个晕属于星系群尺度，各自包含至少1.7亿个粒子，且在最内侧半径处，其密度剖面的斜率相较于-1更为平缓。此外，研究还发现暗物质晕浓度参数（halo concentration）与晕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（power law）描述；基于Navarro等人提出的Press-Schechter理论（Press-Schechter theory）构建的简单模型，与该依赖关系的吻合度较高。自旋参数（spin parameter）与暗物质晕质量则未表现出明显相关性。对于质量大于~10^8倍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（log-normal distribution）得到良好拟合。次晕（subhalo）丰度与暗物质晕质量相关：星系尺度的暗物质晕所拥有的次晕数量，比~10^11倍太阳质量的暗物质晕多50%。本数据集为2048³分辨率模拟集合的第152个快照。