On the duration of the embedded phase of star formation
On the duration of the embedded phase of star formation
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DOI：
10.1093/mnras/stab878
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发表时间：
2020-11
影响因子：
4.8
通讯作者：
Jaeyeon Kim;M. Chevance;J. Kruijssen;A. Schruba;K. Sandstrom;A. Barnes;F. Bigiel;G. Blanc;
中科院分区：
文献类型：
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作者：
Jaeyeon Kim;M. Chevance;J. Kruijssen;A. Schruba;K. Sandstrom;A. Barnes;F. Bigiel;G. Blanc;
来自大质量恒星的反馈在分子云演化中起着关键作用。恒星形成开始后，年轻的恒星群体会受到光电离、风、超新星和来自大质量恒星的辐射压力的影响。最近对附近星系的观测提供了分子云和暴露的年轻恒星之间的演化时间表，但大质量恒星形成的嵌入阶段的持续时间仍然不受限制。我们用CO、Spitzer 2 4、Mu m和Hα分别作为分子云、嵌入恒星形成和裸露恒星形成的示踪剂，对附近6个星系在2 0 0-10 0mbox 1 0 0 mPc分辨率下，用统计方法测量了大质量恒星群在其诞生的星云中停留了多久。我们发现，嵌入相(有CO和24$rm，um$排放)持续2−7Myr，占云寿命的$17-47{rm%}$。在这一阶段的大约前半部分，该区域在Hα中是不可见的，因此它被严重遮挡。在此阶段的后半部分，该区域也以Hα发射，并部分暴露。一旦云层通过反馈被驱散，24毫米米的辐射不再跟踪正在进行的恒星形成，但通过环境中CO-暗气体的发射，跟踪最近结束的恒星形成，仍然可以检测到另一个2−9 MIR。大质量恒星形成的持续时间很短，这表明超新星前的反馈(光电离和风)在破坏分子云方面很重要。所测量的时间尺度与环境属性(例如，金属丰度)没有明显的相关性。未来的JWST观测将使这些测量能够在附近的星系群中进行常规测量。
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 $20{-}100~\mbox{${\rm ~pc}$}$ resolution, using CO, Spitzer 24$\rm \, \mu m$, and H α 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 $17{-}47{{\ \rm per\ cent}}$ of the cloud lifetime. During approximately the first half of this phase, the region is invisible in H α, making it heavily obscured. For the second half of this phase, the region also emits in H α 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 time-scales do not show significant correlations with environmental properties (e.g. metallicity). Future JWST observations will enable these measurements routinely across the nearby galaxy population.