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arXiv 0904.0213astro-ph.GAastro-ph.CO
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银河系中H2/HI-Ratio的宇宙衰落

The Cosmic Decline in the H2/HI-Ratio in Galaxies

D. Obreschkow, S. Rawlings

摘要:

我们使用一个基于压力的模型,将冷氢分裂成原子(HI)和分子(H2)组分,以解决千禧年模拟中~ 3e 7模拟星系中HI,H2和恒星形成率(SFR)的共同演化问题。主要的预测是,星系包含类似数量的HI在红移z=1-5比今天,但实质上更多的H2,在定量协议与强分子线发射已经检测到在一些高红移星系和近似一致的推断从阻尼莱曼α吸收器的研究中看到的类星体的光谱。宇宙中的H2/HI比被预测为单调地演化为Ω(H2)/Ω(HI)(1+z)^[1.6]。这种下降的H2/HI比作为宇宙时间的函数是由星系盘的增长和平均冷气体压力的逐步减少。最后,HI、H2和SFR演化的比较揭示了恒星形成的两个不同的宇宙时期:早期(z>3),由Omega(HI+H2)演化驱动,晚期(z<3),由Omega(H2)/Omega(HI)演化驱动。

英文摘要:

We use a pressure-based model for splitting cold hydrogen into its atomic (HI) and molecular (H2)components to tackle the co-evolution of HI, H2, and star formation rates (SFR) in ~3e7 simulated galaxies in the Millennium simulation. The main prediction is that galaxies contained similar amounts of HI at redshift z=1-5 than today, but substantially more H2, in quantitative agreement with the strong molecular line emission already detected in a few high redshift galaxies and approximately consistent with inferences from studies of the damped Lyman-alpha absorbers seen in the spectra of quasars. The cosmic H2/HI-ratio is predicted to evolve monotonically as Omega(H2)/Omega(HI) (1+z)^1.6. This decline of the H2/HI-ratio as a function of cosmic time is driven by the growth of galactic disks and the progressive reduction of the mean cold gas pressure. Finally, a comparison between the evolutions of HI, H2, and SFRs reveals two distinct cosmic epochs of star formation: an early epoch (z>3), driven by the evolution of Omega(HI+H2), and a late epoch (z<3), driven by the evolution of Omega(H2)/Omega(HI).

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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