The Major Sources of the Cosmic Reionizing Background at z ≃ 6
The Major Sources of the Cosmic Reionizing Background at z ≃ 6
复制标题
z ≃ 6 处宇宙再电离背景的主要来源
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
R. Windhorst
中科院分区：
文献类型：
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作者：
Haojing Yan;R. Windhorst
在这封信中，我们将讨论哪些来源贡献了大部分的再电离光子。我们的论点假设再电离在z 106左右结束，并且这是一个相对较快的过程，即，在宇宙的更早时期，中性氢的比例不可忽略。从我们早先对z = 6的星系的光度函数（LF）的估计出发，我们定量地表明，主要的再电离源最有可能是L < L* 的星系。我们的方法使我们能够把更强的约束在z = 6的星系LF。为了使宇宙在这个红移完全电离，LF的暗端斜率应该比α =-1.6更陡，这是在较低的红移（z = 3）测量的值，除非LF的归一化（Φ*）或电离氢的聚集因子被显著低估。如果Φ* 实际上比我们假设的值低2倍，则需要接近α = -2.0的陡斜率。我们的LF预测，在哈勃太空望远镜超深场中，AB = 28.4等的深度，总共有50-80个z 6星系，这可以用来限制Φ* 和α。我们的结论是，存在于这个红移的最不明亮的星系应该达到一些临界光度低，以积累整个再电离光子预算。另一方面，在稍早的时期存在大量的中性氢，例如，z ≥ 7，要求最不亮的星系不应比另一个临界值暗（即，LF应在此时切断）。
In this Letter, we address which sources contributed most of the reionizing photons. Our argument assumes that the reionization ended around z ≃ 6 and that it was a relatively quick process, i.e., that there was a nonnegligible fraction of neutral hydrogen in the universe at somewhat earlier epochs. Starting from our earlier estimate of the luminosity function (LF) of galaxies at z ≃ 6, we quantitatively show that the major sources of reionization are most likely galaxies with L < L*. Our approach allows us to put stronger constraints to the LF of galaxies at z ≃ 6. To have the universe completely ionized at this redshift, the faint-end slope of the LF should be steeper than α = -1.6, which is the value measured at lower redshifts (z ≃ 3), unless either the normalization (Φ*) of the LF or the clumping factor of the ionized hydrogen has been significantly underestimated. If Φ* is actually lower than what we assumed by a factor of 2, a steep slope close to α = -2.0 is required. Our LF predicts a total of 50-80 z ≃ 6 galaxies in the Hubble Space Telescope Ultra Deep Field to a depth of AB = 28.4 mag, which can be used to constraint both Φ* and α. We conclude that the least luminous galaxies existing at this redshift should reach as low as some critical luminosity in order to accumulate the entire reionizing photon budget. On the other hand, the existence of significant amounts of neutral hydrogen at slightly earlier epochs, e.g., z ≃ 7, requires that the least luminous galaxies should not be fainter than another critical value (i.e., the LF should cut off at this point).