The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-432)

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 432 of the 2048³ resolution collection.

本研究展示了基于标准Λ冷暗物质（LCDM）模型的「宇宙网格（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）的立方体计算盒中完成，共包含2048³个粒子，单个粒子质量为1.28×10^5太阳质量（Msun），该分辨率足以解析超暗矮星系。研究发现，暗物质晕（halo）质量函数在低至约10^7太阳质量（Msun）的范围内，与谢斯-托尔曼（Sheth & Tormen）拟合函数吻合良好。本研究分析了三个质量最大的星系群级暗物质晕的球对称平均密度剖面，这三个晕均包含至少1.7亿个粒子；在最内侧半径处，这些密度剖面的斜率相较于-1更为平缓。同时，研究还发现暗物质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表述，但由纳瓦罗等人（Navarro et al.）基于普雷斯-谢赫特（Press-Schechter）理论提出的简单模型，与该依赖关系的契合度较高。自旋参数与暗物质晕质量则未表现出明显相关性。对于质量大于约10^8太阳质量（Msun）的暗物质晕而言，其浓度参数与自旋参数的概率分布函数均能通过对数正态分布得到良好拟合。次晕丰度与暗物质晕质量密切相关：星系尺度的暗物质晕所含次晕数量，相较约10^11太阳质量（Msun）的暗物质晕多出50%。本数据为2048³分辨率系列模拟的第432号快照。