Measuring the H i Content of Individual Galaxies Out to the Epoch of Reionization with [C ii]
Measuring the H i Content of Individual Galaxies Out to the Epoch of Reionization with [C ii]
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DOI：
10.3847/1538-4357/ac2231
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发表时间：
2021-08
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影响因子：
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通讯作者：
K. Heintz;D. Watson;P. Oesch;D. Narayanan;S. Madden
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作者：
K. Heintz;D. Watson;P. Oesch;D. Narayanan;S. Madden
H i气体含量是星系演化的一个关键因素，由于超精细H i 21 cm跃迁的弱点，对H i气体含量的研究仅限于中等宇宙学距离的单个星系。在这里，我们提出了一种新的方法，使我们能够推断的H i气体质量M HI的个别星系到z <$6的基础上，直接测量的[C ii]到H i转换因子的恒星形成星系在z <$2使用γ射线爆发余辉。通过汇编最近的[C ii]-158 μm发射线测量结果，我们定量地研究了星系中H i含量在宇宙时间中的演化.我们发现M HI在z = 1时开始超过恒星质量M HI，并随着红移的增加而增加。H i占重子总质量的比例从z = 0时的20%增加到z = 6时的60%。我们进一步揭示了氢气体分数MHI/MHI与气相金属丰度之间的普遍关系，这似乎是从z = 6到z = 0。观察到z > 2的大多数星系的H i耗尽时间t dep，HI = M HI/SFR，小于≈2 Gyr，比z 0星系短得多。最后，我们使用[C ii]到H i的转换因子来确定星系中H i的宇宙质量密度ρ HI，在三个不同的时期：z <$0，z <$2和z <$4 -6。这些测量结果与先前基于局域宇宙中21 cm H i观测和z = 2的阻尼Lyα吸收体（DLAs）的估计一致，表明从再电离时期结束到现在，ρ HI（z）总体上下降了1/15。
The H i gas content is a key ingredient in galaxy evolution, the study of which has been limited to moderate cosmological distances for individual galaxies due to the weakness of the hyperfine H i 21 cm transition. Here we present a new approach that allows us to infer the H i gas mass M HI of individual galaxies up to z ≈ 6, based on a direct measurement of the [C ii]-to-H i conversion factor in star-forming galaxies at z ≳ 2 using γ-ray burst afterglows. By compiling recent [C ii]-158 μm emission line measurements we quantify the evolution of the H i content in galaxies through cosmic time. We find that M HI starts to exceed the stellar mass M ⋆ at z ≳ 1, and increases as a function of redshift. The H i fraction of the total baryonic mass increases from around 20% at z = 0 to about 60% at z ∼ 6. We further uncover a universal relation between the H i gas fraction M HI/M ⋆ and the gas-phase metallicity, which seems to hold from z ≈ 6 to z = 0. The majority of galaxies at z > 2 are observed to have H i depletion times, t dep,HI = M HI/SFR, less than ≈2 Gyr, substantially shorter than for z ∼ 0 galaxies. Finally, we use the [C ii]-to-H i conversion factor to determine the cosmic mass density of H i in galaxies, ρ HI, at three distinct epochs: z ≈ 0, z ≈ 2, and z ∼ 4–6. These measurements are consistent with previous estimates based on 21 cm H i observations in the local universe and with damped Lyα absorbers (DLAs) at z ≳ 2, suggesting an overall decrease by a factor of ≈5 in ρ HI(z) from the end of the reionization epoch to the present.