The lifecycle of molecular clouds in nearby star-forming disc galaxies
The lifecycle of molecular clouds in nearby star-forming disc galaxies
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DOI：
10.1093/mnras/stz3525
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发表时间：
2019-11
影响因子：
4.8
通讯作者：
M. Chevance;D. Kruijssen;A. Hygate;A. Schruba;S. Longmore;B. Groves;J. Henshaw;C. Herrera;A. H
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文献类型：
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作者：
M. Chevance;D. Kruijssen;A. Hygate;A. Schruba;S. Longmore;B. Groves;J. Henshaw;C. Herrera;A. H
导出云尺度（$\lesssim100$ pc）恒星形成和反馈的理论仍然是一个主要的挑战，描述星系如何将气体转化为恒星作为星系环境的函数。由于缺乏对巨分子云（GMC）生命周期的强有力的经验约束，进展受到阻碍。我们通过系统地应用一种新的统计方法来测量GMC生命周期、恒星形成的演化时间线，并反馈到作为PHANGS-ALMA调查的一部分观察到的9个附近盘状星系的样本来解决这个问题。我们测量了空间分辨（～ 100pc） CO-to-H α通量比，发现分子气体和年轻恒星在GMC尺度上普遍不相关，使我们能够量化潜在的进化时间。GMC的寿命很短，通常是$10\!-\!30\,{\rm Myr}$，并且在星系之间和星系内部表现出环境变化。在kpc尺度的分子气体表面密度$\Sigma _{\rm H_2}\ge 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$下，GMC寿命与星系动力学过程的时间尺度相关，而在$\Sigma _{\rm H_2}\le 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$下，GMC与星系动力学解耦，并为内部动力学时间尺度而存在。经过长时间的惰性阶段，没有大质量恒星的形成（由H α追踪）（云寿命的75 - 90％），一旦大质量恒星出现，gmc就会分散在$1\!-\!5\,{\rm Myr}$内。分散最有可能是由于早期的恒星反馈，导致gmc达到4 - 10％的综合恒星形成效率。这些结果表明，银河系恒星形成是由云尺度、环境依赖、驱动快速进化循环的动态过程控制的。gmc和H ii区域是经历这些生命周期的基本单位，在恒星形成盘中平均间隔为$100\!-\!300\,{{\rm pc}}$。未来的工作应该描述驱动这些生命周期的多尺度物理和质量流。
It remains a major challenge to derive a theory of cloud-scale ($\lesssim100$ pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically $10\!-\!30\,{\rm Myr}$, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities $\Sigma _{\rm H_2}\ge 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at $\Sigma _{\rm H_2}\le 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75–90 per cent of the cloud lifetime), GMCs disperse within just $1\!-\!5\,{\rm Myr}$ once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4–10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H ii regions are the fundamental units undergoing these lifecycles, with mean separations of $100\!-\!300\,{{\rm pc}}$ in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.