Implementation of metals in a three-dimensional non-LTE radiative transfer code to simulate the intergalactic medium at early cosmological times

现代天体物理学研究的一个重要问题是精确地理解宇宙演化的早期阶段。最近对大尺度结构形成的研究表明，直接由原始气体形成的第一代恒星在宇宙再电离时代的早期阶段已经发挥了关键作用。理论研究表明，这第一个恒星群体的初始质量函数（IMF）与现在的IMF有很大不同，头重脚轻，因此允许超大质量恒星的存在。因此，第一代第三星族恒星不仅非常明亮，而且由于缺乏金属，其紫外辐射的输出大大超过了现在恒星的紫外辐射。由于它们的寿命很短，核心中产生的金属很快就返回到环境中，形成了具有不同IMF和不同光谱能量分布（SED）的早期第二星族恒星，早于宇宙完全再电离的时间（在z > 6的红移）。在拟议的项目中，我们的目标是计算不同金属丰度的超大质量恒星的SED，作为3-三维辐射传输代码，我们目前正在开发模拟电离的非均匀星际和星系间介质的时间演化，使用多个恒星集群作为电离辐射源。其目的不仅是模拟据信导致宇宙再电离状态的过程，而且是确定可能的观测诊断，以限制电离源的性质。我们结合三维辐射转移-基于射线追踪-和对所有重要元素-包括金属-的电离结构的随时间变化的模拟进行的多频处理，原则上将能够推断出关于第一代恒星的光谱特征及其在各种尺度上与周围气体的相互作用的信息。由于我们的工具将能够处理以高分辨率合成SED为特征的众多辐射源的分布，（因此，我们将不简单地使用"黑体“光谱），并且还将产生将在NLTE中处理并与三维辐射传递一致地计算的元素的最重要能级的占据数，将更准确地计算非均匀气体密度结构的电离状态。在此基础上，我们将系统地研究从III族星到II/I族星过渡过程中辐射源（模拟星团结构）金属丰度的增加对星际和星系间介质电离结构的影响。

An important issue in modern astrophysical research is to understand precisely the early phases of the evolution of the universe. Recent studies investigating the formation of large-scale structures have shown that the first generation of stars, formed directly from the primordial gas, already played a crucial role during the early phase of the epoch of reionization of the universe. Theoretical studies indicate that the initial mass function (IMF) of this first stellar population differed significantly from the present IMF, being top-heavy and thus allowing for the presence of supermassive stars. The first generation of population III stars was therefore not only very luminous, but due to its lack of metals its output of UV radiation considerably exceeded the UV emission of present stars. Because of their short lifetimes the metals produced in their cores were quickly returned to the environment from which early population II stars with different IMFs and different spectral energy distributions (SEDs) were formed, already much earlier than the time at which the universe became completely reionized (at a redshift of z > 6).In the proposed project we aim to calculate SEDs of very massive stars of different metallicities as input for the 3-dimensional radiative transfer code we are currently developing to simulate the temporal evolution of the ionization of the inhomogeneous interstellar and intergalactic medium, using multiple stellar clusters as sources of ionizing radiation. The objective is not only to simulate the processes which are believed to have lead to the reionized state of the universe, but also to determine possible observational diagnostics to constrain the nature of the ionizing sources. The multi-frequency treatment in our combination of 3-dimensional radiative transfer -- based on ray-tracing -- and time dependent simulation of the ionization structure of all important elements -- including metals -- will allow, in principle, to deduce information about the spectral characteristics of the first generations of stars and their interaction with the surrounding gas on various scales. As our tool will be able to handle distributions of numerous radiative sources characterized by high resolution synthetic SEDs (we will thus not simply use ``black-body'' spectra), and will also yield occupation numbers of the most important energy levels of the elements which will be treated in NLTE and calculated consistently with the 3-dimensional radiative transfer, the ionization state of an inhomogeneous gaseous density structure will be calculated more accurately. On basis of this procedure we will systematically investigate the impact of the increasing metallicity of the radiative sources (simulated cluster structures) in the transition from population III stars to population II/I stars on the ionization structure of the interstellar and intergalactic medium.