Three-dimensional modeling of ionized gas - I. Did very massive stars of different metallicities drive the second cosmic reionization?
Three-dimensional modeling of ionized gas - I. Did very massive stars of different metallicities drive the second cosmic reionization?
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DOI：
10.1051/0004-6361/201220897
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发表时间：
2013-04
影响因子：
6.5
通讯作者：
J. A. Weber;A. Pauldrach;J. S. Knogl;T. Hoffmann
中科院分区：
文献类型：
--
作者：
J. A. Weber;A. Pauldrach;J. S. Knogl;T. Hoffmann
直接由原始气体形成的第一代恒星在宇宙再电离的早期阶段发挥了关键作用。由于这些恒星的寿命很短，核心产生的金属很快就返回到环境中，形成了具有不同初始质量函数和不同SED的早期PopII恒星，这比宇宙在z~6的红移下完全再电离的时间要早得多。使用一个国家的最先进的模型大气代码，我们计算现实的SED的超大质量恒星（VMSs）的不同金属丰度作为输入的3维多频辐射传输代码，我们已经开发了模拟的时间演变的不均匀的星际和星系间介质的电离，使用多个星团作为电离辐射源。我们的工具处理分布的许多辐射源的特点是高分辨率的合成SED，并产生所需的能量水平的最重要的元素，在NLTE处理一致的三维辐射传输的占用数。我们进一步证明，从PopIII星到PopII星的过渡中的辐射源的金属丰度的增加对发射光谱的硬度有很强的影响，因此对氦的再电离历史。在高核质量密度的化学演化星系团中形成的顶重恒星质量分布不仅可能提供中等质量和超大质量黑洞（SMBH）的祖先，而且还对HeII的再电离起着重要作用。如果假设银河系SMBH是由较小的黑洞合并形成的，那么用z~2.5的红移来修正HeII所需的VMS的数量与解释银河系SMBH所需的VMS的数量非常接近。
The first generation of stars that formed directly from the primordial gas played a crucial role in the early phase of the reionization of the universe. Because of the short lifetimes of these stars the metals produced in their cores were quickly returned to the environment, from which early PopII stars with a different initial mass function and different SEDs were formed, already much earlier than the time at which the universe became completely reionized at a redshift of z~6. Using a state-of-the-art model atmosphere code we calculate realistic SEDs of very massive stars (VMSs) of different metallicities to serve as input for the 3-dimensional multi-frequency radiative transfer code we have developed to simulate the temporal evolution of the ionization of the inhomogeneous interstellar and intergalactic medium, using multiple stellar clusters as sources of ionizing radiation. Our tool handles distributions of numerous radiative sources characterized by high resolution synthetic SEDs, and yields occupation numbers of the required energy levels of the most important elements which are treated in NLTE consistently with the 3d radiative transfer. We further demonstrate that the increasing metallicity of the radiative sources in the transition from PopIII stars to PopII stars has a strong impact on the hardness of the emitted spectrum, and hence on the reionization history of helium. A top-heavy stellar mass distribution characterized by VMSs forming in chemically evolved clusters of high core mass density may not only provide the progenitors of intermediate-mass and supermassive black holes (SMBHs), but also play an important role for the reionization of HeII. The number of VMSs required to reionize HeII by a redshift of z~2.5 is astonishingly close to the number of VMSs required to explain galactic SMBHs if one assumes that these have been formed by mergers of smaller black holes.