Giant molecular clouds (GMCs) and their stellar offspring are the building blocks of galaxies. The physical characteristics of GMCs and their evolution are tightly connected to galaxy evolution. The macroscopic properties of the interstellar medium propagate into the properties of GMCs condensing out of it, with correlations between e.g. the galactic and GMC scale gas pressures, surface densities and volume densities. That way, the galactic environment sets the initial conditions for star formation within GMCs. After the onset of massive star formation, stellar feedback from e.g. photoionisation, stellar winds, and supernovae eventually contributes to dispersing the parent cloud, depositing energy, momentum and metals into the surrounding medium, thereby changing the properties of galaxies. This cycling of matter between gas and stars, governed by star formation and feedback, is therefore a major driver of galaxy evolution. Much of the recent debate has focused on the durations of the various evolutionary phases that constitute this cycle in galaxies, and what these can teach us about the physical mechanisms driving the cycle. We review results from observational, theoretical, and numerical work to build a dynamical picture of the evolutionary lifecycle of GMC evolution, star formation, and feedback in galaxies.

中文翻译：

---

分子云生命周期

巨型分子云 (GMC) 及其恒星后代是星系的基石。GMC 的物理特性及其演化与星系演化密切相关。星际介质的宏观性质传播到从其中凝结出来的 GMC 的性质中，例如银河和 GMC 尺度的气体压力、表面密度和体积密度之间存在相关性。这样，银河环境就为 GMC 内的恒星形成设定了初始条件。在大质量恒星形成开始后，来自例如光电离、恒星风和超新星的恒星反馈最终有助于分散母云，将能量、动量和金属沉积到周围介质中，从而改变星系的性质。这种气体和恒星之间的物质循环，受恒星形成和反馈控制，因此是星系演化的主要驱动力。最近的大部分辩论都集中在构成星系循环的各种演化阶段的持续时间，以及这些可以告诉我们什么关于驱动这个循环的物理机制。我们回顾了观测、理论和数值工作的结果，以构建 GMC 演化、恒星形成和星系反馈的演化生命周期的动态图景。