Observations that resolve nearby galaxies into individual regions across multiple phases of the gas–star formation–feedback “matter cycle” have provided a sharp new view of molecular clouds, star-formation efficiencies, timescales for region evolution, and stellar feedback. We synthesize these results, covering aspects relevant to the interpretation of observables, and conclude the following: ▪ The observed cloud-scale molecular gas surface density, line width, and internal pressure all reflect the large-scale galactic environment while also appearing mostly consistent with properties of a turbulent medium strongly affected by self-gravity. ▪ Cloud-scale data allow for statistical inference of both evolutionary and physical timescales. These suggest a period of cloud collapse on the order of the free-fall or turbulent crossing time (∼10–30 Myr) followed by forming massive stars and subsequent rapid (≲5 Myr) gas clearing after the onset of star formation. The star-formation efficiency per free-fall time is well determined over thousands of individual regions at εff ≈ 0.5−0.3 +0.7%. ▪ The role of stellar feedback is now measured using multiple observational approaches. The net yield is constrained by the requirement to support the vertical weight of the galaxy disk. Meanwhile, the short gas-clearing timescales suggest a large role for presupernova feedback in cloud disruption. This leaves the supernovae free to exert a large influence on the larger galaxy, including stirring turbulence, launching galactic-scale winds, and carving superbubbles.

中文翻译：

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附近星系云尺度上的分子气体和恒星形成过程


在气体-恒星形成-反馈“物质周期”的多个阶段中，将附近的星系分解为单个区域的观测为分子云、恒星形成效率、区域演化的时间尺度和恒星反馈提供了清晰的新视角。我们综合了这些结果，涵盖了与解释可观测物相关的方面，并得出以下结论：▪观测到的云尺度分子气体表面密度、线宽和内部压力都反映了大尺度的银河系环境，同时也与受自身引力强烈影响的湍流介质的特性基本一致。▪ 云规模的数据允许对进化和物理时间尺度进行统计推断。这些表明，在恒星形成开始后，云层会以自由落体或湍流穿越时间（∼10-30 Myr）的顺序坍缩，然后形成大质量恒星，随后迅速（≲5 Myr）气体清除。在 εff ≈ 0.5-0.3 +0.7% 的数千个单独区域中，每自由落体时间的恒星形成效率得到了很好的确定。▪ 恒星反馈的作用现在使用多种观测方法来衡量。净产额受到支撑星系盘垂直重量的要求的限制。同时，较短的气体清除时间尺度表明，超新星前反馈在云中断中起着重要作用。这使得超新星可以自由地对更大的星系施加很大的影响，包括搅动湍流、发射银河系尺度的风和雕刻超级气泡。