标题： 在恒星形成嵌入阶段的持续时间 显示英文标题

标题： On the duration of the embedded phase of star formation

摘要： 大质量恒星的反馈在分子云演化中起着关键作用。 在恒星形成开始后，年轻的恒星种群会受到大质量恒星的光致电离、风、超新星和辐射压力的影响。 对邻近星系的最新观测提供了分子云和暴露的年轻恒星之间的演化时间线，但大质量恒星形成的嵌入阶段的持续时间仍然无法准确确定。 我们通过将统计方法应用于六个多邻近星系，在20-100 pc的分辨率下，使用CO、斯皮策24$\rm\,\mu m$和H$\alpha$发射作为分子云、嵌入恒星形成和暴露恒星形成的示踪剂，测量了大质量恒星种群在原始云中嵌入的时间。 我们发现，嵌入阶段（具有CO和24$\rm\,\mu m$发射）持续时间为$2{-}7$百万年，并占云寿命的$17{-}47\%$。 在这一阶段的前半部分，该区域在H$\alpha$中不可见，使其被严重遮挡。 在这一阶段的后半部分，该区域也会在H$\alpha$中发射，并且部分暴露。 一旦云被反馈分散，24$\rm\,\mu m$辐射不再追踪持续的恒星形成，但通过周围CO暗气体的辐射，仍可检测到另一个$2{-}9$Myr，追踪最近结束的恒星形成。 大质量恒星形成的短暂持续时间表明，超新星前反馈（电离和风）在破坏分子云中起着重要作用。 测量的时间尺度与环境特性（例如金属量）没有显著相关性。 未来的JWST观测将使这些测量在附近星系群体中常规化。 显示英文摘要

摘要： Feedback from massive stars plays a key role in molecular cloud evolution. After the onset of star formation, the young stellar population is exposed by photoionization, winds, supernovae, and radiation pressure from massive stars. Recent observations of nearby galaxies have provided the evolutionary timeline between molecular clouds and exposed young stars, but the duration of the embedded phase of massive star formation is still ill-constrained. We measure how long massive stellar populations remain embedded within their natal cloud, by applying a statistical method to six nearby galaxies at 20-100 pc resolution, using CO, Spitzer 24$\rm\,\mu m$, and H$\alpha$ emission as tracers of molecular clouds, embedded star formation, and exposed star formation, respectively. We find that the embedded phase (with CO and 24$\rm\,\mu m$ emission) lasts for $2{-}7$ Myr and constitutes $17{-}47\%$ of the cloud lifetime. During approximately the first half of this phase, the region is invisible in H$\alpha$, making it heavily obscured. For the second half of this phase, the region also emits in H$\alpha$ and is partially exposed. Once the cloud has been dispersed by feedback, 24$\rm\,\mu m$ emission no longer traces ongoing star formation, but remains detectable for another $2{-}9$ Myr through the emission from ambient CO-dark gas, tracing star formation that recently ended. The short duration of massive star formation suggests that pre-supernova feedback (photoionization and winds) is important in disrupting molecular clouds. The measured timescales do not show significant correlations with environmental properties (e.g. metallicity). Future JWST observations will enable these measurements routinely across the nearby galaxy population.