引力捕获与风压捕获超紧致和超紧致的H II区域
Gravitational trapping and ram pressure trapping of ultracompact and hypercompact H II regions
AI总结：
研究通过模拟H II区域的引力和风压捕获机制，揭示了不同密度条件下H II区域的生长停滞现象及寿命问题。
摘要：
观测上，早期的H II区域根据大小被分为超紧致和超紧致的配置。这些阶段是否长期存在还是短暂的仍不清楚。理解阻碍H II区域增长的物理过程可能有助于解决所谓的寿命问题：观测到的H II区域比理论预期更紧致。利用二维、轴对称的辐射流体动力学模拟，包括早期恒星和盘形成阶段，我们试图更好地理解H II区域的捕获。捕获力包括引力和风压，这些力与热压膨胀、辐射压和离心力等力相反对。没有辐射压，H II区域会无限期地被引力捕获在超紧致阶段。有辐射压时，H II区域会逃离引力捕获，但在更大尺度上经历风压捕获。对于初始质量库具有高中心密度时，没有捕获发生，而较陡的密度梯度会产生明显的被捕获阶段。超紧致被捕获阶段表现出H II区域半径的所谓闪烁变化，这与观测到的停滞甚至在小时间尺度上的收缩一致。有辐射压时，低密度库经历引力和风压捕获，而高质量库仅经历后者。
英文摘要：
Observationally, early H II regions are classified by size into ultracompact and hypercompact configurations. It remains unclear whether these phases are long-lived or transient. Understanding the physical processes that stall H II region growth may help to solve the so-called lifetime problem: the observation of more compact H II regions than expected from theory. Utilizing two-dimensional, axially symmetric radiation hydrodynamic simulations of young expanding H II regions, including the phase of early star and disk formation, we seek to better understand the trapping of H II regions. Trapping forces include gravity and ram pressure, which oppose forces such as thermal pressure expansion, radiation pressure, and centrifugal force. Without radiation pressure, the H II region remains gravitationally trapped in the ultracompact phase indefinitely. With radiation pressure, the H II region escapes gravitational trapping but experiences ram pressure trapping on larger scales. For initial mass reservoirs with high central density, no trapping occurs, while a less steep density gradient yields clear trapped phases. Hypercompact trapped phases exhibit a so-called flickering variation in H II region radius, in agreement with observations of stalling and even contraction over small time scales. With radiation pressure, low-density reservoirs experience both gravitational and ram pressure trapping, while high-mass reservoirs undergo only the latter.
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