Simulating cosmic reionization at large scales – II. The 21-cm emission features and statistical signals
Simulating cosmic reionization at large scales – II. The 21-cm emission features and statistical signals
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DOI：
10.1111/j.1365-2966.2006.10919.x
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发表时间：
2006-03
影响因子：
4.8
通讯作者：
G. Mellema;I. Iliev;U. Pen;P. R. S. Astron;S. Leiden;Cita;D. Astronomy;U. Austin
中科院分区：
文献类型：
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作者：
G. Mellema;I. Iliev;U. Pen;P. R. S. Astron;S. Leiden;Cita;D. Astronomy;U. Austin
我们提出了从再电离时代红移21厘米信号的详细预测。这些预测是根据大尺度（100 h -1 Mpc）、高动态范围、宇宙学模拟的结果进行辐射传递计算得到的。我们考虑了再电离历史的几种情景，包括早期和延长的再电离。通过模拟，我们构建并分析了一系列观测特征，从全局信号，通过详细的图像和光谱，到均方根波动的统计表示，角功率谱和概率分布函数，以表征21厘米信号的非高斯性。我们发现，不同的再电离情景产生相当相似的观测特征，主要不同于50%再电离的红移和最终重叠。所有情景都显示平均信号和均方根波动的全球特征逐渐转变，这将使这些更难以观察。个别特征，如深的间隙和明亮的峰，与平均值有很大的不同，用几弧分和100秒的千赫分辨率来绘制这些特征，将提供对潜在密度场和宇宙H II区域几何形状的直接测量，尽管由于特殊的速度扭曲而有很大的修改。后期发射峰的存在表明这些是观测的有用目标。再电离过程中的功率谱与潜在的密度波动相比有很大的提高。最强的统计信号出现在50%再电离时，并在1 ~ 3000-5000角尺度上显示出明显的最大值。我们发现发射特征的分布函数是强非高斯分布，明亮发射特征的概率要高一个数量级。这些结果表明，在观测上，可能比推导功率谱更容易找到单个明亮特征，而功率谱又比观测单个图像更容易。
We present detailed predictions for the redshifted 21-cm signal from the epoch of reionization. These predictions are obtained from radiative transfer calculations on the results of large-scale (100 h -1 Mpc), high dynamic range, cosmological simulations. We consider several scenarios for the reionization history, of both early and extended reionizations. From the simulations, we construct and analyse a range of observational characteristics, from the global signal, via detailed images and spectra, to statistical representations of rms fluctuations, angular power spectra, and probability distribution functions to characterize the non-Gaussianity of the 21-cm signal. We find that the different reionization scenarios produce quite similar observational signatures, mostly differing in the redshifts of 50 per cent reionization, and of final overlap. All scenarios show a gradual transition in the global signatures of mean signal and rms fluctuations, which would make these more difficult to observe. Individual features, such as deep gaps and bright peaks, are substantially different from the mean, and mapping these with several arcminutes and 100 s of kHz resolution would provide a direct measurement of the underlying density field and the geometry of the cosmological H II regions, although significantly modified by peculiar velocity distortions. The presence of late emission peaks suggests these to be a useful target for observations. The power spectra during reionization are strongly boosted compared to the underlying density fluctuations. The strongest statistical signal is found around the time of 50 per cent reionization and displays a clear maximum at an angular scale of l ∼ 3000-5000. We find the distribution function of emission features to be strongly non-Gaussian, with an order of magnitude higher probability of bright emission features. These results suggest that, observationally, it may be easier to find individual bright features than deriving the power spectra, which, in turn, is easier than observing individual images.