The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-537)

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 537 of the 2048³ resolution collection.

本研究展示基于一致性Λ冷暗物质（LCDM）模型的“宇宙网格（Cosmogrid）”宇宙学N体模拟套件的结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方盒中完成，共包含2048³个粒子，单个粒子的质量为1.28×10^5倍太阳质量（Msun），足以分辨超暗矮星系（ultra-faint dwarfs）。我们发现，晕质量函数与希斯-托门（Sheth & Tormen）拟合函数在低至~10^7倍太阳质量（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级晕的球对称平均密度剖面，这些晕属于星系群尺度，且至少包含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更平缓。同时我们还发现，晕浓度（halo concentration）与晕质量存在显著相关性：浓度参数的质量依赖关系无法用单一幂律（power law）描述，但基于纳瓦罗等人（Navarro et al.）提出的普雷斯-谢赫特（Press-Schechter）理论构建的简单模型，与该依赖关系吻合良好。自旋参数（spin parameter）与晕质量不存在相关性。对于质量大于~10^8倍太阳质量（Msun）的晕，其浓度和自旋的概率分布函数均可用对数正态分布（log-normal distribution）很好地拟合。子晕丰度与晕质量相关：星系尺度的晕所拥有的子晕数量比~10^11倍太阳质量（Msun）的晕多50%。本数据集为2048³分辨率模拟序列中的第537个快照。