The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-566)

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 566 of the 2048³ resolution collection.

本研究展示了基于标准Λ冷暗物质（LCDM）模型的“Cosmogrid”宇宙学N体模拟套件的相关结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方盒中开展，总粒子数达2048³。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。研究发现，晕质量函数与谢斯-托尔门（Sheth & Tormen）拟合公式在低至~10^7 Msun的范围内均保持良好一致性。我们分析了三个质量最大的星系群尺度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变得比-1更为平缓。同时我们发现晕的集中度与质量存在显著相关性。集中度参数的质量依赖关系无法用单一幂律描述，但基于纳瓦罗等人提出的普雷斯-谢赫特（Press-Schechter）理论的简单模型与该依赖关系吻合良好。自旋参数与晕质量则无明显相关性。对于质量大于~10^8 Msun的晕，其集中度和自旋参数的概率分布函数均可通过对数正态分布实现良好拟合。次晕丰度随晕质量变化：星系级晕的次晕数量比~10^11 Msun级晕多50%。本数据集为2048³分辨率模拟集合的第566个快照。