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arXiv 2108.01074astro-ph.GAastro-ph.CO
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再电离时期高${\rm [OIII]}_{\rm 88μm}$ / ${\rm [CII]}_{\rm 158μm}$半导体的性质：低碳半导体和头重脚轻的IMF？

The Nature of High ${\rm [OIII]}_{\rm 88μm}$/${\rm [CII]}_{\rm 158μm}$ Galaxies in the Epoch of Reionization: Low Carbon Abundance and a Top-Heavy IMF?

Harley Katz, Joakim Rosdahl, Taysun Kimm, Thibault Garel, Jérémy Blaizot, Martin G. Haehnelt, Léo Michel-Dansac, Sergio Martin-Alvarez, Julien Devriendt, Adrian… 展开作者

Harley Katz, Joakim Rosdahl, Taysun Kimm, Thibault Garel, Jérémy Blaizot, Martin G. Haehnelt, Léo Michel-Dansac, Sergio Martin-Alvarez, Julien Devriendt, Adrianne Slyz, Romain Teyssier, Pierre Ocvirk, Nicolas Laporte, Richard Ellis

备注：
20 pages, 18 figures, Accepted by MNRAS
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摘要：

对$z>6$星系的ALMA观测显示，与本地星系相比，[OIII] $_{\rm 88μm}$ /[CII] $_{\rm 158μm}$比值和[CII] $_{\rm 158μm}$赤字异常高。已经提出了许多解决方案，包括C和O丰度比的差异，观测偏差和ISM属性的差异。为了阐明驱动这种高红移现象的基本物理，我们采用SPHINX $^{20}$，一个国家的最先进的，宇宙辐射流体动力学模拟，解决了详细的ISM属性的数千个星系的再电离时代。我们发现，所观察到的$z>6$ [OIII]-SFR和[CII]-SFR的关系，只有当C/O丰度比是$\sim8\times$低于太阳能和总金属产量是$\sim4\times$高于Kroupa IMF的。这意味着高红移星系可能主要是由具有更头重脚轻IMF的低金属量核心坍缩超新星富集的。当AGB星和Ia型超新星开始对星系金属丰度产生贡献时，[CII]-SFR和[CII]光度函数都将在$z\sim4.5$处收敛到观测值。虽然我们证明了电离参数，LyC逃逸分数，ISM气体密度和CMB衰减都驱动星系朝向更高的[OIII]/[CII]，在$z>6$观察到的值只能复制与太阳相比，大大降低C/O丰度。[CII]和[OIII]的组合可用于预测电离参数、ISM气体密度和LyC逃逸分数的值，我们提供了九个观测到的$z>6$星系的这些量的估计。最后，我们证明了[OI] $_{\rm 63μm}$可以在[CII]未被观测到的高红移星系中作为[CII]的替代，并认为应该用更多的观测时间将[OI]对准$z>6$。（节录）

英文摘要：

ALMA observations of $z>6$ galaxies have revealed abnormally high [OIII]$_{\rm 88μm}$/[CII]$_{\rm 158μm}$ ratios and [CII]$_{\rm 158μm}$ deficits compared to local galaxies. Numerous solutions have been proposed including differences in C and O abundance ratios, observational bias, and differences in ISM properties. In order to elucidate the underlying physics that drives this high-redshift phenomenon, we employ SPHINX$^{20}$, a state-of-the-art, cosmological radiation-hydrodynamics simulation, that resolves detailed ISM properties of thousands of galaxies in the epoch of reionization. We find that the observed $z>6$ [OIII]-SFR and [CII]-SFR relations can only be reproduced when the C/O abundance ratio is $\sim8\times$ lower than Solar and the total metal production is $\sim4\times$ higher than that of a Kroupa IMF. This implies that high-redshift galaxies are potentially primarily enriched by low-metallicity core-collapse supernovae with a more top-heavy IMF. As AGB stars and type-Ia supernova begin to contribute to the galaxy metallicity, both the [CII]-SFR and [CII] luminosity functions are predicted to converge to observed values at $z\sim4.5$. While we demonstrate that ionisation parameter, LyC escape fraction, ISM gas density, and CMB attenuation all drive galaxies towards higher [OIII]/[CII], observed values at $z>6$ can only be reproduced with substantially lower C/O abundances compared to Solar. The combination of [CII] and [OIII] can be used to predict the values of ionisation parameter, ISM gas density, and LyC escape fraction and we provide estimates of these quantities for nine observed $z>6$ galaxies. Finally, we demonstrate that [OI]$_{\rm 63μm}$ can be used as a replacement for [CII] in high-redshift galaxies where [CII] is unobserved and argue that more observation time should be used to target [OI] at $z>6$. (Abridged)

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