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arXiv 0906.4552astro-ph.CO
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宇宙近红外背景II:涨落

The Cosmic Near Infrared Background II: Fluctuations

Elizabeth R. Fernandez, Eiichiro Komatsu, Ilian T. Iliev, Paul R. Shapiro

摘要:

近红外背景(NIRB)是少数几种可以用来观测早期恒星红移6及以上的方法之一。NIRB的起伏可以提供关于IGM中第一结构的信息,例如晕及其周围的电离区域。我们首次将N体模拟、辐射转移程序和早期结构光度的解析计算结合起来,预测了NIRB中涨落的角功率谱(C_l)。我们研究了恒星质量、恒星初始质量谱、金属丰度、恒星形成效率(f_*)、电离光子逃逸率(f_esc)和恒星形成时标(t_SF)等各种假设对C_l振幅和形状的影响。当f_* 最大(当C_l ~(f_*)^2时),f_esc最小时,NIRB波动的功率谱最大。由于我们对这些星系的t_SF缺乏了解,这相当于我们对质光比缺乏了解,因此C_l的预测振幅存在很大的不确定性。我们没有看到一个营业额在NIRB角功率谱的晕贡献,并解释这是高水平的非线性偏置的影响。这部分是由于我们选择的最小质量的晕有助于NIRB,和一个较小的最小质量,它有一个较小的非线性偏差,可能仍然表现出一个翻转。因此,无论是振幅和形状的NIRB功率谱提供了重要的信息,对宇宙再电离源的性质作出贡献。在大多数情况下,IGM的角功率谱远小于晕的角功率谱。此外,低水平的观测平均背景强度往往排除高值的f_* > 0.2。

英文摘要:

The Near Infrared Background (NIRB) is one of a few methods that can be used to observe the redshifted light from early stars at a redshift of six and above. Fluctuations of the NIRB can provide information on the first structures, such as halos and their surrounding ionized regions in the IGM. We combine, for the first time, N-body simulations, radiative transfer code, and analytic calculations of luminosity of early structures to predict the angular power spectrum (C_l) of fluctuations in the NIRB. We study the effects of various assumptions about the stellar mass, the initial mass spectrum of stars, metallicity, the star formation efficiency (f_*), the escape fraction of ionizing photons (f_esc), and the star formation timescale (t_SF), on the amplitude as well as the shape of C_l. The power spectrum of NIRB fluctuations is maximized when f_* is the largest (as C_l ~ (f_*)^2) and f_esc is the smallest. A significant uncertainty in the predicted amplitude of C_l exists due to our lack of knowledge of t_SF of these galaxies, which is equivalent to our lack of knowledge of the mass-to-light ratio. We do not see a turnover in the NIRB angular power spectrum of the halo contribution and explain this as the effect of high levels of non-linear bias. This is partly due to our choice of the minimum mass of halos contributing to NIRB, and a smaller minimum mass, which has a smaller non-linear bias, may still exhibit a turn over. Therefore, both the amplitude and shape of the NIRB power spectrum provide important information regarding the nature of sources contributing to the cosmic reionization. The angular power spectrum of the IGM, in most cases, is much smaller than the halo angular power spectrum. In addition, low levels of the observed mean background intensity tend to rule out high values of f_* > 0.2.

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