The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-728)

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 728 of the 2048³ resolution collection.

本研究呈现基于标准Λ冷暗物质（Lambda Cold Dark Matter, ΛCDM）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（megaparsec, Mpc）的周期性模拟箱中完成，总粒子数为2048³。单个粒子质量为1.28×10^5 Msun，该分辨率足以解析超暗矮星系（ultra-faint dwarfs）。研究发现，晕质量函数与Sheth & Tormen拟合公式吻合良好，该吻合度可覆盖至约10^7 Msun的质量范围。我们对三个质量最大的星系群级晕开展了球对称平均密度剖面分析，每个晕至少包含1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率相较于-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。不过集中度参数的质量依赖关系无法用单一幂律函数描述，而基于Press-Schechter理论、由Navarro等人提出的简化模型则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。对于质量大于约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（log-normal distribution）很好地拟合。次晕丰度同样依赖于晕质量：星系尺度的晕相较于约10^11 Msun的晕，其所含次晕数量多出50%。本数据集为2048³分辨率模拟集的第728个快照。