The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-561)

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 561 of the 2048³ resolution collection.

本研究展示了基于一致性Λ冷暗物质（LCDM）模型的“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）的模拟箱中完成，总粒子数达2048³。每个粒子的质量为1.28×10^5倍太阳质量（Msun），该分辨率足以解析超暗矮星系（ultra-faint dwarfs）。我们发现，暗物质晕质量函数（halo mass function）在低至约10^7倍太阳质量的范围内，与Sheth-Tormen拟合公式（Sheth & Tormen fitting function）吻合良好。我们分析了三个质量最大的星系群尺度暗物质晕的球对称平均密度剖面（spherically averaged density profiles），这三个晕至少包含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，暗物质晕集中度（halo concentration）与质量存在显著相关性。集中度参数（concentration parameter）的质量依赖性无法用单一幂律（power law）描述，但基于Navarro等人（Navarro et al.）提出的普雷斯-谢赫特理论（Press-Schechter theory）构建的简单模型，与该依赖性的吻合度较好。自旋参数（spin parameter）与暗物质晕质量并无相关性。对于质量大于约10^8倍太阳质量的暗物质晕，其集中度和自旋参数的概率分布函数（probability distribution functions）均可用对数正态分布（log-normal distribution）良好拟合。次晕丰度（subhalo abundance）随暗物质晕质量变化：星系级暗物质晕的次晕数量比约10^11倍太阳质量的晕多50%。本数据为2048³分辨率模拟集合的第561个快照。