标题： 来自高红移的21厘米背景辐射 显示英文标题

标题： The Global 21 Centimeter Background from High Redshifts

摘要： 我们研究了结构形成早期阶段平均天空21厘米背景的演化。使用简单的解析模型，我们计算了热历史和电离历史，假设恒星光子主导辐射背景。 由此产生的21厘米频谱可以限制第一代恒星和类星体的性质。如果第二代恒星占主导地位，Lyman-alpha耦合使得IGM在被X射线加热之前以及再电离之前可见。因此，21厘米背景有一个强吸收时期，随后是变弱的发射，在再电离期间逐渐消失。非常大质量的第三代恒星的硬谱压缩这些转变到较短的时间间隔并降低信号幅度。然而，再电离时期仍将是可见的，除非在极端情况下。由于天文学前景，全球21厘米信号将难以观测，但它提供了一个研究最早光源的令人兴奋的机会。它还固定了波动背景的整体幅度，其检测是几个下一代低频射电干涉仪的主要目标之一。 显示英文摘要

摘要： We consider the evolution of the sky-averaged 21 cm background during the early phases of structure formation. Using simple analytic models, we calculate the thermal and ionization histories, assuming that stellar photons dominate the radiation background. The resulting 21 cm spectra can constrain the properties of the first generations of stars and quasars. If Population II stars dominate, Lyman-alpha coupling renders the IGM visible before it is heated by X-rays and long before reionization. Thus the 21 cm background has a strong absorption epoch followed by weaker emission that fades during reionization. The harder spectra of very massive Population III stars compress these transitions into a shorter time interval and decreases the signal amplitude. However, the reionization epoch will remain visible except in extreme cases. The global 21 cm signal will be challenging to observe because of astronomical foregrounds, but it offers an exciting opportunity to study the first sources of light. It also fixes the overall amplitude of the fluctuating background whose detection is a major goal of several next-generation low-frequency radio interferometers.