论文标题
在z $ \ simeq $ 6星系中跟踪分子气，使用[c $ {\ rm \ scriptsize ii} $]
Tracing Molecular Gas in z $\simeq$ 6 Galaxies with [C${\rm \scriptsize II}$]
论文作者
论文摘要
我们通过分析分子气体质量（$ m _ {\ rm mol} $）和[c $ {c $ {\ rm \ rm \ rm \ rm \ rm \ rm \ rm \ rm，rm r c（l II ii ii} $ rm rim r c（l r c r r r c r r r c $ rm ii ii} $ rm， [CII]} $）在11,125 $ z \ simeq 6 $ star形成，来自Simba模拟的主要序列星系，并由Sígame建模线排放。尽管我们的模拟中的大多数（$ \ sim 50-100 \，\％$）是离子化的，但[C $ {\ rm \ rm \ scriptsize ii} $]的散装（$> 50 \，\％$）来自分子阶段。我们发现了一个子线性（坡度$ 0.78 \ pm 0.01 $）$ \ log l _ {\ rm [cii]} - \ log m _ {\ rm mol} $的关系，与从更大的，金属富裕的金属的观测样品中得出的线性关系是$ z \ z \ sim $ z \ 6 $ 6 $ 6 $ 6 $ 6 $的线性关系。我们得出一个中位数[c $ {\ rm \ scriptsize ii} $] - to- $ m _ {\ rm mol} $转换因子为$α_ {\ rm [cii]} \ simeq 18 \ \ \，{\ rm m _ {\ rm m _ {\ rm \ odot} $ _ {这低于$ \ simeq 30 \的平均值，{\ rm m _ {\ rm \ odot}/l _ {\ rm \ odot}} $衍生自观测，我们将其归因于我们的模拟中的气体型金属度。因此，从[C $ {\ rm \ rm \ Scriptsize II} $]观测到低质量星系的观测值时，必须应用较低的光度依赖性，转化因子。对于我们的模拟，[c $ {\ rm \ scriptsize ii} $]是分子气的更好的示踪剂，而co $ j = 1-0 $，尤其是在最低金属性的情况下，大部分气体是“ co-doc”。我们发现，$ l _ {\ rm [cii]} $与$ m _ {\ rm mol} $更紧密地相关，而与星形构型率（$ {\ rm sfr} $）和$ \ log log l _ {\ rm [cii]} - \ rm [cii]} - \ log m molm and $ and \ rmm molm和rm rmm an l _ {\ rm [cii]} - \ log {\ rm sfr} $关系来自kennicutt-schmidt关系。我们的发现表明，$ l _ {\ rm [cii]} $是最早的宇宙时代的分子气体的有前途的示踪剂。
We investigate the fine-structure [C${\rm \scriptsize II}$] line at $158\,μ$m as a molecular gas tracer by analyzing the relationship between molecular gas mass ($M_{\rm mol}$) and [C${\rm \scriptsize II}$] line luminosity ($L_{\rm [CII]}$) in 11,125 $z\simeq 6$ star-forming, main sequence galaxies from the SIMBA simulations, with line emission modeled by SÍGAME. Though most ($\sim 50-100\,\%$) of the gas mass in our simulations is ionized, the bulk ($> 50\,\%$) of the [C${\rm \scriptsize II}$] emission comes from the molecular phase. We find a sub-linear (slope $0.78\pm 0.01$) $\log L_{\rm [CII]}-\log M_{\rm mol}$ relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at $z \lesssim 6$. We derive a median [C${\rm \scriptsize II}$]-to-$M_{\rm mol}$ conversion factor of $α_{\rm [CII]} \simeq 18\,{\rm M_{\rm \odot}/L_{\rm \odot}}$. This is lower than the average value of $\simeq 30\,{\rm M_{\rm \odot}/L_{\rm \odot}}$ derived from observations, which we attribute to lower gas-phase metallicities in our simulations. Thus, a lower, luminosity-dependent, conversion factor must be applied when inferring molecular gas masses from [C${\rm \scriptsize II}$] observations of low-mass galaxies. For our simulations, [C${\rm \scriptsize II}$] is a better tracer of the molecular gas than CO $J=1-0$, especially at the lowest metallicities, where much of the gas is 'CO-dark'. We find that $L_{\rm [CII]}$ is more tightly correlated with $M_{\rm mol}$ than with star-formation rate (${\rm SFR}$), and both the $\log L_{\rm [CII]}-\log M_{\rm mol}$ and $\log L_{\rm [CII]}-\log {\rm SFR}$ relations arise from the Kennicutt-Schmidt relation. Our findings suggest that $L_{\rm [CII]}$ is a promising tracer of the molecular gas at the earliest cosmic epochs.
