Star Formation Efficiency and Dispersal of Giant Molecular Clouds with UV Radiation Feedback: Dependence on Gravitational Boundedness and Magnetic Fields
Star Formation Efficiency and Dispersal of Giant Molecular Clouds with UV Radiation Feedback: Dependence on Gravitational Boundedness and Magnetic Fields
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DOI：
10.3847/1538-4357/abe934
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发表时间：
2020-11
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影响因子：
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通讯作者：
Jeong-Gyu Kim;E. Ostriker;N. Filippova
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作者：
Jeong-Gyu Kim;E. Ostriker;N. Filippova
分子云受到湍流和磁场的支持，但量化它们对云的生命周期和恒星形成效率(SFE)的影响仍然是一个悬而未决的问题。我们对具有紫外光反馈的恒星形成的巨型分子云(GMC)进行了辐射磁流体力学模拟，其中UV辐射的传播通过光线跟踪与氢光化学耦合。我们考虑了10个GMC模型，它们的初始维里参数(1≤αVIR，0≤5)或无量纲质磁通量比(0.5≤μΦ，0≤8和∞)变化，初始质量为105M⊙，半径为20pC。每个模型运行五种不同的初始湍流实现。在大多数模型中，恒星形成的持续时间和分子气体去除(主要是通过光蒸发)的时间尺度是4-8 Myr。最终超临界流体能量(ε*)和每自由落体时间的时间平均超临界流体能量(εff)都受到强湍流和强磁场的影响。中位数ε*介于2.1%至9.5%之间。中位数εff在1.0%~8.0%之间，与αVIR为0呈反相关，与已有的解析理论和模拟结果定性一致。然而，由于快速演化，基于瞬时气体性质和星团光度的含时αVIR(T)和εff，obs(T)是正相关的，这使得恒星形成理论的观测验证变得困难。我们的中位数εff，obs(T)≈2%与观测值相似。我们发现，传统的维里参数估计的真引力有界性平均在2倍以内，但忽略磁支撑和速度各向异性有时会导致与传统维里参数估计的很大偏差。磁性亚临界GMC不太可能代表大质量恒星形成的地点，因为它们不切实际的柱状流出，延长的寿命和低辐射逃逸分数。
Molecular clouds are supported by turbulence and magnetic fields, but quantifying their influence on cloud life cycle and star formation efficiency (SFE) remains an open question. We perform radiation magnetohydrodynamic simulations of star-forming giant molecular clouds (GMCs) with UV radiation feedback, in which the propagation of UV radiation via ray tracing is coupled to hydrogen photochemistry. We consider 10 GMC models that vary in either initial virial parameter (1 ≤ α vir,0 ≤ 5) or dimensionless mass-to-magnetic flux ratio (0.5 ≤ μ Φ,0 ≤ 8 and ∞ ); the initial mass 105 M ⊙ and radius 20 pc are fixed. Each model is run with five different initial turbulence realizations. In most models, the duration of star formation and the timescale for molecular gas removal (primarily by photoevaporation) are 4–8 Myr. Both the final SFE (ε *) and time-averaged SFE per freefall time (ε ff) are reduced by strong turbulence and magnetic fields. The median ε * ranges between 2.1% and 9.5%. The median ε ff ranges between 1.0% and 8.0%, and anticorrelates with α vir,0, in qualitative agreement with previous analytic theory and simulations. However, the time-dependent α vir(t) and ε ff,obs(t) based on instantaneous gas properties and cluster luminosity are positively correlated due to rapid evolution, making observational validation of star formation theory difficult. Our median ε ff,obs(t) ≈ 2% is similar to observed values. We show that the traditional virial parameter estimates the true gravitational boundedness within a factor of 2 on average, but neglect of magnetic support and velocity anisotropy can sometimes produce large departures from traditional virial parameter estimates. Magnetically subcritical GMCs are unlikely to represent sites of massive star formation given their unrealistic columnar outflows, prolonged lifetime, and low escape fraction of radiation.