The physics and early history of the intergalactic medium
The physics and early history of the intergalactic medium
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DOI：
10.1088/0034-4885/70/4/r02
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发表时间：
2006-11
影响因子：
18.1
通讯作者：
R. Barkana;A. Loeb
中科院分区：
文献类型：
--
作者：
R. Barkana;A. Loeb
星系间介质--充满星系之间巨大空间的宇宙气体--受到一系列过程的影响，从非常早期宇宙的量子波动到新形成的恒星的辐射发射。这给了星际介质双重作用，既是基础物理的强大探测器，也是天体物理的探测器。基础物理学的标题包括宇宙非常早期的条件和决定宇宙年龄及其物质含量的宇宙学参数。天体物理学指的是恒星和星系的漫长宇宙历史中的章节，这些章节是通过恒星对宇宙气体的反馈效应来揭示的。这篇综述描述了星系间介质的物理学，重点介绍了在理解早期宇宙历史方面的最新理论和观测进展。特别是，最早的一代恒星被认为将宇宙从黑暗转变为光明，并对星际介质产生了巨大的影响。大爆炸发生50万年后，宇宙充满了原子氢。当引力将气体云聚集在一起时，第一批恒星被点燃，它们的辐射将周围的原子重新转变为自由电子和离子。从观测到的我们和遥远来源之间气体的光谱吸收特征，我们知道在大爆炸后10亿年，再电离过程弥漫在大部分太空中，因此只有一小部分原始氢原子留在星系之间。准确地知道再电离过程发生的时间和方式是宇宙学家的主要目标，因为这将告诉我们早期的恒星和黑洞是何时形成的，以及在什么类型的星系中形成的。这些星系的分布和星团是特别有趣的，因为它是由暗物质中的原始密度波动驱动的。在理论模型和计算机模拟的帮助下，人们开始理解宇宙再电离。再电离的数值模拟在计算上具有挑战性，因为它们需要跨大宇宙体积的辐射传输以及足够高的分辨率来确定婴儿宇宙中的电离辐射源。随着更多的观测投入，我们的理解有望迅速取得进展。目前正在设计的各种仪器--包括地面或空间大口径红外望远镜(JWST)，以及用于探测红移21厘米辐射的低频射电望远镜阵列--将探测到宇宙历史上一个很大程度上迄今尚未探索的时代的第一批光源。新的观测结果以及对理论模型和数值模拟的挑战将推动未来十年在这一领域的紧张工作。
The intergalactic medium—the cosmic gas that fills the great spaces between the galaxies—is affected by processes ranging from quantum fluctuations in the very early Universe to radiative emission from newly formed stars. This gives the intergalactic medium a dual role as a powerful probe both of fundamental physics and of astrophysics. The heading of fundamental physics includes conditions in the very early Universe and cosmological parameters that determine the age of the Universe and its matter content. The astrophysics refers to chapters of the long cosmic history of stars and galaxies that are being revealed through the effects of stellar feedback on the cosmic gas. This review describes the physics of the intergalactic medium, focusing on recent theoretical and observational developments in understanding early cosmic history. In particular, the earliest generation of stars is thought to have transformed the Universe from darkness to light and to have had an enormous impact on the intergalactic medium. Half a million years after the Big Bang the Universe was filled with atomic hydrogen. As gravity pulled gas clouds together, the first stars ignited and their radiation turned the surrounding atoms back into free electrons and ions. From the observed spectral absorption signatures of the gas between us and distant sources, we know that the process of reionization pervaded most of space a billion years after the Big Bang, so that only a small fraction of the primordial hydrogen atoms remained between galaxies. Knowing exactly when and how the reionization process happened is a primary goal of cosmologists, because this would tell us when the early stars and black holes formed and in what kinds of galaxies. The distribution and clustering of these galaxies is particularly interesting since it is driven by primordial density fluctuations in the dark matter. Cosmic reionization is beginning to be understood with the help of theoretical models and computer simulations. Numerical simulations of reionization are computationally challenging, as they require radiative transfer across large cosmological volumes as well as sufficiently high resolution to identify the sources of the ionizing radiation in the infant Universe. Rapid progress in our understanding is expected with additional observational input. A wide variety of instruments currently under design—including large-aperture infrared telescopes on the ground or in space (JWST), and low-frequency radio telescope arrays for the detection of redshifted 21 cm radiation—will probe the first sources of light during an epoch in cosmic history that has been largely unexplored so far. The new observations and the challenges for theoretical models and numerical simulations will motivate intense work in this field over the coming decade.