Intense C iv and He ii Emission in z ∼ 0 Galaxies: Probing High-energy Ionizing Photons
Intense C iv and He ii Emission in z ∼ 0 Galaxies: Probing High-energy Ionizing Photons
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z 〜 0 星系中的强烈 C iv 和 He ii 发射：探测高能电离光子
DOI：
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发表时间：
2019
影响因子：
4.9
通讯作者：
G. Olivier
中科院分区：
文献类型：
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作者：
D. Berg;J. Chisholm;D. Erb;R. Pogge;A. Henry;G. Olivier
在过去的几年中，在z ~ 5-7星系的深紫外光谱中观测到突出的高电离星云发射线（即O iii]， C iii]， C iv和He ii），表明极端辐射场是再电离时代系统的特征。这些谱线在理论上和观测上都与莱曼连续体光子的泄漏（再电离所必需的）有关。因此，高电离紫外线发射线提供了我们最好的探测器来探测和表征我们将在未来几年观测到的最遥远的星系，并且是理解再电离来源的关键，然而控制它们产生的物理学知之甚少。在这里，我们展示了最近两个附近的极紫外发射线星系J104457和J141851的高分辨率哈勃太空望远镜光谱。我们报告了强烈的星云He ii和双峰共振散射的C iv发射的首次观测，这一组合表明这些星系通过相对较低的高电离气体柱密度产生并传输了大量的高能电离光子（E > 47.89 eV）。这表明，除了在h电离边缘的光子外，从这些星系中逃逸出来的非常坚硬的电离光子可能提供了目前观测上不受约束的二次电离源。需要Lyα和c4的同步辐射传输模型来了解电离辐射如何通过低电离和高电离气体传输。未来使用詹姆斯·韦伯太空望远镜或超大型望远镜（elt）对再电离时期的星系进行静止框架远紫外观测，将使我们能够限制氦电离光子的逃逸，并提供它们对再电离预算的贡献的估计。
In the last few years, prominent high-ionization nebular emission lines (i.e., O iii], C iii], C iv, and He ii) have been observed in the deep UV spectra of z ∼ 5–7 galaxies, indicating that extreme radiation fields characterize reionization-era systems. These lines have been linked to the leakage of Lyman continuum photons (necessary for reionization) both theoretically and observationally. Consequently, high-ionization UV emission lines present our best probe to detect and characterize the most distant galaxies that we will observe in the coming years, and are key to understanding the sources of reionization, yet the physics governing their production is poorly understood. Here we present recent high-resolution Hubble Space Telescope spectra of two nearby extreme UV emission-line galaxies, J104457 and J141851. We report the first observations of intense nebular He ii and double-peaked, resonantly scattered C iv emission, a combination that suggests these galaxies both produce and transmit a significant number of very high-energy ionizing photons (E > 47.89 eV) through relatively low column densities of high-ionization gas. This suggests that, in addition to photons at the H-ionizing edge, the very hard ionizing photons that escape from these galaxies may provide a secondary source of ionization that is currently unconstrained observationally. Simultaneous radiative transfer models of Lyα and C iv are needed to understand how ionizing radiation is transmitted through both low- and high-ionization gas. Future rest-frame far-UV observations of galaxies within the epoch of reionization using the James Webb Space Telescope or extremely large telescopes (ELTs) will allow us to constrain the escape of helium-ionizing photons and provide an estimate for their contribution to the reionization budget.