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arXiv 1410.2249astro-ph.GA
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星系际电离背景的平坦性和突变性

The Flatness and Sudden Evolution of the Intergalactic Ionizing Background

Joseph A. Muñoz, S. Peng Oh, Frederick B. Davies, Steven R. Furlanetto

备注：
16 pages, 7 figures, submitted to MNRAS, revised methods leading to same but more convincing conclusions
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摘要：

宇宙氢的电离本底是探测再电离后宇宙电离辐射源和吸收体的重要手段。以前的研究表明，电离率应该是非常敏感的源人口的变化：随着发射率的上升，吸收体的尺寸缩小，增加电离平均自由程，因此，电离背景。相比之下，电离背景的观测发现从z~2-5的演变非常平坦，然后在z~6处急剧下降。我们解决了这个令人困惑的矛盾，指出，在z~2-5，光学厚吸收体与相同的崩溃晕宿主电离源。因此，星系丰度的增加被吸收体数量的相应增加所补偿，这缓和了电离背景的不稳定性。而当z~5-6时，晕外的气体占主导地位，源与吸收体之间的耦合消失，电离背景迅速演化。我们的基于晕的模型再现了电离背景的观测，它的平坦度和突然下降，以及电离平均自由程的红移演化，我们的工作表明，通过它们的历史，在宇宙中的恒星形成和光电不透明度跟踪晕的增长。

英文摘要：

The ionizing background of cosmic hydrogen is an important probe of the sources and absorbers of ionizing radiation in the post-reionization universe. Previous studies show that the ionization rate should be very sensitive to changes in the source population: as the emissivity rises, absorbers shrink in size, increasing the ionizing mean free path and, hence, the ionizing background. By contrast, observations of the ionizing background find a very flat evolution from z~2-5, before falling precipitously at z~6. We resolve this puzzling discrepancy by pointing out that, at z~2-5, optically thick absorbers are associated with the same collapsed halos that host ionizing sources. Thus, an increasing abundance of galaxies is compensated for by a corresponding increase in the absorber population, which moderates the instability in the ionizing background. However, by z~5-6, gas outside of halos dominates the absorption, the coupling between sources and absorbers is lost, and the ionizing background evolves rapidly. Our halo based model reproduces observations of the ionizing background, its flatness and sudden decline, as well as the redshift evolution of the ionizing mean free path. Our work suggests that, through much of their history, both star formation and photoelectric opacity in the universe track halo growth.

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