分子云生命周期II：通过H$_2$荧光发射诊断分子云的形成与毁灭
The Molecular Cloud Lifecycle II: Formation and Destruction of Molecular Clouds Diagnosed via H$_2$ Fluorescent Emission Emission
AI总结：
本研究利用SILCC模拟，通过H$_2$形成与离解速率诊断分子云生命周期，提出空间FUV光谱仪观测可区分云构建、快速恒星形成、化学平衡及云毁灭等阶段。
摘要：
分子氢（H$_2$）的形成与离解是驱动星系中气体生命周期的关键过程。利用模拟分子云生命周期（SILCC）的放大模拟套件，我们探讨了未来对H$_2$离解与形成的观测在追踪分子云生命周期中的效用。本工作使用的模拟包括非平衡H$_2$形成、恒星辐射、汇聚粒子和湍流。我们发现，在云演化的早期阶段，H$_2$形成迅速超过离解，分子云从环境中的原子储库积累质量。快速的H$_2$形成也与较高的早期恒星形成率相关。对于所研究的云，在云形成的早期阶段，H$_2$强烈偏离化学平衡，但在首批恒星形成后约2百万年，进入一种爆发性的化学稳态。在云演化的最新阶段，离解超过形成，云进入消散阶段。我们讨论了如何通过空间高分辨率远紫外光谱仪（如提议的NASA探索者任务Hyperion和Eos）对H$_2$荧光的观测测量来区分分子云生命周期和恒星形成效率的理论。此类任务将能够测量H$_2$离解和形成速率，我们证明这些速率可以与分子云恒星形成生命中的不同阶段相关联，包括云构建、快速恒星形成、H$_2$化学平衡和云毁灭。
英文摘要：
Molecular hydrogen (H$_2$) formation and dissociation are key processes that drive the gas lifecycle in galaxies. Using the SImulating the LifeCycle of Molecular Clouds (SILCC) zoom-in simulation suite, we explore the utility of future observations of H$_2$ dissociation and formation for tracking the lifecycle of molecular clouds. The simulations used in this work include non-equilibrium H$_2$ formation, stellar radiation, sink particles, and turbulence. We find that, at early times in the cloud evolution, H$_2$ formation rapidly outpaces dissociation and molecular clouds build their mass from the atomic reservoir in their environment. Rapid H$_2$ formation is also associated with a higher early star formation rate. For the clouds studied here, H$_2$ is strongly out of chemical equilibrium during the early stages of cloud formation but settles into a bursty chemical steady-state about 2 Myrs after the first stars form. At the latest stage of cloud evolution, dissociation outweighs formation and the clouds enter a dispersal phase. We discuss how theories for the molecular cloud lifecycle and the star formation efficiency may be distinguished with observational measurements of H$_2$ fluorescence with a space-based high-resolution FUV spectrometer, such as the proposed Hyperion and Eos NASA Explorer missions. Such missions would enable measurements of the H$_2$ dissociation and formation rates, which we demonstrate can be connected to different phases in a molecular cloud's star-forming life, including cloud building, rapidly star-forming, H$_2$ chemical equilibrium, and cloud destruction.
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