Signals from the epoch of cosmological recombination – Karl Schwarzschild Award Lecture 2008
Signals from the epoch of cosmological recombination – Karl Schwarzschild Award Lecture 2008
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DOI：
10.1002/asna.200911237
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发表时间：
2009-08
影响因子：
0.9
通讯作者：
R. Sunyaev;J. Chluba
中科院分区：
文献类型：
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作者：
R. Sunyaev;J. Chluba
描述宇宙重组时代的物理成分非常简单，也非常容易理解。这一事实使我们能够考虑到各种各样的物理过程，仍然发现宇宙微波背景（CMB）的能谱和温度各向异性的潜在可测量的后果。在这篇文章中，我们提供了一个简短的历史概述与宇宙重组时代及其连接到CMB。此外，我们强调了一些详细的物理学研究在过去几年中的背景下，宇宙学的氢和氦的重组。这些考虑的影响是双重的：（一）在这一时期相关的光子释放导致宇宙微波背景（CMB）能谱与完美黑体的有趣和独特的偏差，特别是在分米波长和CMB光谱的维恩部分，可能在不久的将来变得可观察到。尽管氦的丰度相当小，但它仍然为完整的复合光谱贡献了相当数量的光子，从而导致额外的独特光谱特征。观测氢和氦复合时期的光谱失真，原则上将提供一种额外的方法来确定宇宙的一些关键参数（例如比熵，CMB的温度和氦的星前丰度）。它还使我们能够用直接的观测证据来对抗我们对复合过程的详细理解。在这方面的贡献，我们说明了如何的理论光谱模板的宇宙复合谱可用于此目的。我们还表明，由于氢和氦在非常不同的时期重新结合，因此有可能解决与我们宇宙的热历史有关的问题。特别是宇宙学复合辐射可以让我们区分康普顿y -扭曲，这是由能量释放之前或之后的宇宙复合完成。(ii)随着高精度CMB数据的出现，例如，将使用普朗克测量者或CMBPOL，一个非常准确的宇宙电离历史的理论理解成为必要的CMB温度和偏振各向异性的解释。在这里，我们表明，电离历史的不确定性，由于几个过程，直到现在还没有考虑到在标准的重组代码RECFAST，达到百分比水平。特别是He II He I复合发生得更快，因为在z = 2400处存在一小部分中性氢。最近还证明，在H I莱曼α光子的情况下，发射过程的时间依赖性以及发射和吸收轮廓之间的不对称性是不能忽略的。然而，宇宙学的重组历史即使在1000万级的精确度下也是如此的惰性，这确实令人惊讶。观察宇宙学复合谱原则上应该允许我们直接检验这个结论，这个结论到目前为止还是纯理论的。还可以允许使用观测数据重建电离历史（© 2009 WILEY-VCH Verlag GmbH & Co. KGaA，魏因海姆）
The physical ingredients to describe the epoch of cosmological recombination are amazingly simple and well-understood. This fact allows us to take into account a very large variety of physical processes, still finding potentially measurable consequences for the energy spectrum and temperature anisotropies of the Cosmic Microwave Background (CMB). In this contribution we provide a short historical overview in connection with the cosmological recombination epoch and its connection to the CMB. Also we highlight some of the detailed physics that were studied over the past few years in the context of the cosmological recombination of hydrogen and helium. The impact of these considerations is two-fold: (i) The associated release of photons during this epoch leads to interesting and unique deviations of the CosmicMicrowave Background (CMB) energy spectrum from a perfect blackbody, which, in particular at decimeter wavelength and the Wien part of the CMB spectrum, may become observable in the near future. Despite the fact that the abundance of helium is rather small, it still contributes a sizeable amount of photons to the full recombination spectrum, leading to additional distinct spectral features. Observing the spectral distortions from the epochs of hydrogen and helium recombination, in principle would provide an additional way to determine some of the key parameters of the Universe (e.g. the specific entropy, the CMB monopole temperature and the pre-stellar abundance of helium). Also it permits us to confront our detailed understanding of the recombination process with direct observational evidence. In this contribution we illustrate how the theoretical spectral template of the cosmological recombination spectrum may be utilized for this purpose. We also show that because hydrogen and helium recombine at very different epochs it is possible to address questions related to the thermal history of our Universe. In particular the cosmological recombination radiation may allow us to distinguish between Compton y -distortions that were created by energy release before or after the recombination of the Universe finished. (ii) With the advent of high precision CMB data, e.g. as will be available using the PLANCK Surveyor or CMBPOL, a very accurate theoretical understanding of the ionization history of the Universe becomes necessary for the interpretation of the CMB temperature and polarization anisotropies. Here we show that the uncertainty in the ionization history due to several processes, which until now were not taken in to account in the standard recombination code RECFAST, reaches the percent level. In particular He II He I recombination occurs significantly faster because of the presence of a tiny fraction of neutral hydrogen at z ∼ 2400. Also recently it was demonstrated that in the case of H I Lyman α photons the timedependence of the emission process and the asymmetry between the emission and absorption profile cannot be ignored. However, it is indeed surprising how inert the cosmological recombination history is even at percent-level accuracy. Observing the cosmological recombination spectrum should in principle allow us to directly check this conclusion, which until now is purely theoretical. Also it may allow to reconstruct the ionization history using observational data (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)