Tracing Molecular Gas Mass in z ≃ 6 Galaxies with [C ii]
Tracing Molecular Gas Mass in z ≃ 6 Galaxies with [C ii]
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DOI：
10.3847/1538-4357/ac5cba
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发表时间：
2022-03
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通讯作者：
D. Vizgan;T. Greve;K. Olsen;A. Zanella;D. Narayanan;R. Davé;G. Magdis;G. Popping;F. Valentino;K. Heintz
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作者：
D. Vizgan;T. Greve;K. Olsen;A. Zanella;D. Narayanan;R. Davé;G. Magdis;G. Popping;F. Valentino;K. Heintz
通过分析simba模拟的11，125个z <$6恒星形成的主序星星系中分子气体质量（M mol）和[C ii]线光度（L [C II]）之间的关系，研究了158 μm处精细结构[C ii]线作为分子气体示踪剂的情况。虽然在我们的模拟中，大部分（约50%-100%）的气体质量是电离的，但大部分（>50%）的[C ii]发射来自分子相。我们发现了一个次线性（斜率为0.78 ± 0.01）logL[CII]-logMmol关系，与来自更大质量、富含金属的星系在z = 6的观测样本的线性关系相反。我们推导出[C II]-至-M mol转换因子的中位数为α [C II]<$18 M <$/L <$。这低于从观测中得出的平均值1030 M/L，我们将其归因于模拟中较低的气相金属丰度。因此，一个较低的，亮度依赖的转换因子时，必须应用推断分子气体质量从[C二]观测低质量星系。对于我们的模拟，[C ii]是一个更好的示踪剂的分子气体比CO J = 1-0，特别是在最低的金属丰度，其中大部分的气体是CO暗。我们发现L [CII]与M mol的相关性比与星星形成率（SFR）的相关性更强，并且logL[CII]-logMmol和logL[CII]-logSFR关系都来源于Kennicutt-Schmidt关系.我们的研究结果表明，L [C II]是一个有前途的示踪剂的分子气体在最早的宇宙时代。
We investigate the fine-structure [C ii] line at 158 μm as a molecular gas tracer by analyzing the relationship between molecular gas mass (M mol) and [C ii] line luminosity (L [C II]) in 11,125 z ≃ 6 star-forming, main-sequence galaxies from the simba simulations, with line emission modeled by the Simulator of Galaxy Millimeter/Submillimeter Emission. Though most (∼50%–100%) of the gas mass in our simulations is ionized, the bulk (>50%) of the [C ii] emission comes from the molecular phase. We find a sublinear (slope 0.78 ± 0.01) logL[CII]–logMmol relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at z ≲ 6. We derive a median [C ii]-to-M mol conversion factor of α [C II] ≃ 18 M ⊙/L ⊙. This is lower than the average value of ≃30 M ⊙/L ⊙ 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 ii] observations of low-mass galaxies. For our simulations, [C 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 [C II] is more tightly correlated with M mol than with star formation rate (SFR), and both the logL[CII]–logMmol and logL[CII]–logSFR relations arise from the Kennicutt–Schmidt relation. Our findings suggest that L [C II] is a promising tracer of the molecular gas at the earliest cosmic epochs.