Constrained Cosmological Simulations of Dark Matter Halos

The formation and structure of dark matter halos are investigated by means of constrained realizations of Gaussian fields using N-body simulations. Experiments in the formation of a 1012 h-1 M☉ halo are designed to study the dependence of the density profile on its merging history. We find that (1) the halo growth consists of several violent and quiescent phases, with the density well approximated by the Navarro-Frenk-White (NFW) profile at most times; (2) the NFW scale radius Rs stays constant during the quiet phases and grows abruptly during the violent ones, while the virial radius grows linearly during the quiet phases and grows abruptly during the violent phases; (3) the value of Rs reflects the violent merging history of the halo; (4) the central density stays unchanged during the quiet phases while dropping abruptly during the violent ones (its value does not reflect the formation time of the halo); and (5) the clear separation of the evolution of an individual halo into series of quiescent and violent phases explains the inability to fit its entire evolution by simple scaling relations, in agreement with previous studies.

利用N体模拟，通过高斯场的约束实现来研究暗物质晕的形成和结构。设计了形成$10^{12}h^{-1}M_{\odot}$晕的实验，以研究密度剖面与其并合历史的相关性。我们发现：（1）晕的增长包含几个剧烈阶段和宁静阶段，在大多数时候其密度可以很好地用纳瓦罗 - 弗伦克 - 怀特（NFW）剖面来近似；（2）NFW尺度半径$R_s$在宁静阶段保持不变，在剧烈阶段突然增大，而位力半径在宁静阶段线性增长，在剧烈阶段突然增长；（3）$R_s$的值反映了晕的剧烈并合历史；（4）中心密度在宁静阶段保持不变，在剧烈阶段突然下降（其值不反映晕的形成时间）；（5）将单个晕的演化清晰地划分为一系列宁静阶段和剧烈阶段，解释了为何无法用简单的标度关系来拟合其整个演化过程，这与先前的研究一致。