论文标题
恒星形成效率和具有紫外线辐射反馈的巨型分子云的扩散：依赖重力界限和磁场
Star Formation Efficiency and Dispersal of Giant Molecular Clouds with UV Radiation Feedback: Dependence on Gravitational Boundedness and Magnetic Fields
论文作者
论文摘要
分子云由湍流和磁场支持，但量化其对云生命周期和恒星形成效率（SFE）的影响仍然是一个空旷的问题。我们对具有紫外线辐射反馈的恒星形成巨型分子云（GMC）进行辐射MHD模拟，其中通过射线追踪紫外线辐射的传播与氢光化学耦合。我们考虑了10个GMC模型，它们的初始病毒参数（$ 1 \leα_{V，0} \ le 5 $）或无量纲质量磁性通量比（0.5-8和$ \ infty $）有所不同；初始质量$ 10^5M _ {\ odot} $和半径20pc是固定的。每个模型都具有五个不同的初始湍流实现。在大多数模型中，恒星形成的持续时间和去除分子气体的时间尺度（主要通过光蒸发）为4-8myr。最终的SFE（$ε_*$）和每次自由落体时间（$ε_{ff} $）的SFE均通过强湍流和磁场降低。中值$ε_*$在2.1％至9.5％之间。与先前的分析理论和模拟的定性一致性，中位数$ε_{FF} $在1.0％至8.0％之间，并用$α_{V，0} $进行反矫正。但是，基于瞬时气体特性和集群光度的时间依赖性$α_{v}（t）$和$ε_{ff，obs}（t）$由于快速进化而呈正相关，这使得对星形形成理论的观察性验证变得困难。我们的中位数$ε_{ff，obs}（t）\ $ 2％与观察到的值相似。我们表明，传统的病毒参数估算平均2倍的真正重力界限，但是忽略磁支持和速度各向异性有时会产生较大的出发。磁性亚临界GMC不太可能代表大规模恒星形成的部位，因为它们的不现实的柱状柱出口，寿命的延长和辐射的低逃逸部分。
Molecular clouds are supported by turbulence and magnetic fields, but quantifying their influence on cloud lifecycle and star formation efficiency (SFE) remains an open question. We perform radiation MHD 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 ($1\leα_{v,0}\le 5$) or dimensionless mass-to-magnetic flux ratio (0.5-8 and $\infty$); the initial mass $10^5M_{\odot}$ and radius 20pc 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 4-8Myr. 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 $α_{v,0}$, in qualitative agreement with previous analytic theory and simulations. However, the time-dependent $α_{v}(t)$ 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 $ε_{ff,obs}(t)\approx$ 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. 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.
