arXiv 2007.144392020-07-28astro-ph.GA

高红移星系OIII精细结构辐射的解析模型

An analytic model for OIII fine structure emission from high redshift galaxies

Shengqi Yang, Adam Lidz

DOI：: 10.1093/mnras/staa3000

摘要：

最近的ALMA测量揭示了星系在再电离时期（EoR）的明亮OIII 88微米线发射，红移高达$z \sim 9$。我们引入了一个分析模型来帮助解释这些和其他即将到来的OIII 88微米测量。我们的方法总结了从离散Str $\ddot{\mathrm{o}}$ mgren球的发射，并认为在一个给定的恒星形成率的星系中的电离氢的总体积。我们估计了双电离氧和电离氢的相对体积及其对电离光子谱的依赖性。然后，我们计算的水平人口的OIII离子在不同的精细结构状态的HII区域的指定参数。在这个简单的模型中，一个星系的OIII 88微米光度是由以下因素决定的：HII区域中自由电子的典型数密度（$n_e$），这些区域的平均金属丰度（$Z$），氢离子化光子发射的速率（$Q_{\mathrm{HI}}$），以及电离光谱的形状。我们通过将我们的模型与详细的云计算进行比较来交叉检查，发现它在广泛的参数空间范围内的$\%$精度优于15。将我们的模型应用到现有的ALMA数据在$z \sim 6-9$，我们得到的气体金属丰度的下限和气体密度的上限在这些星系的HII区域。这些极限在不同的星系之间有很大的差异，最严格的界限表示$Z \gtrsim 0.5 Z_\odot$和$n_{\mathrm{H}} \lesssim 50$ cm $^{-3}$在$2-σ$置信度下。

英文摘要：

Recent ALMA measurements have revealed bright OIII 88 micron line emission from galaxies during the Epoch of Reionization (EoR) at redshifts as large as $z \sim 9$. We introduce an analytic model to help interpret these and other upcoming OIII 88 micron measurements. Our approach sums over the emission from discrete Str$\ddot{\mathrm{o}}$mgren spheres and considers the total volume of ionized hydrogen in a galaxy of a given star-formation rate. We estimate the relative volume of doubly-ionized oxygen and ionized hydrogen and its dependence on the spectrum of ionizing photons. We then calculate the level populations of OIII ions in different fine-structure states for HII regions of specified parameters. In this simple model, a galaxy's OIII 88 micron luminosity is determined by: the typical number density of free electrons in HII regions ($n_e$), the average metallicity of these regions ($Z$), the rate of hydrogen ionizing photons emitted ($Q_{\mathrm{HI}}$), and the shape of the ionizing spectrum. We cross-check our model by comparing it with detailed CLOUDY calculations, and find that it works to better than 15$\%$ accuracy across a broad range of parameter space. Applying our model to existing ALMA data at $z \sim 6-9$, we derive lower bounds on the gas metallicity and upper bounds on the gas density in the HII regions of these galaxies. These limits vary considerably from galaxy to galaxy, with the tightest bounds indicating $Z \gtrsim 0.5 Z_\odot$ and $n_{\mathrm{H}} \lesssim 50$ cm$^{-3}$ at $2-σ$ confidence.

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