标题： 分子云的年龄和恒星形成时间尺度的观测限制：磁扩散控制还是湍流诱导的恒星形成？ 显示英文标题

标题： Observational Constraints on the Ages of Molecular Clouds and the Star-Formation Timescale: Ambipolar-Diffusion--Controlled or Turbulence-Induced Star Formation?

摘要： 我们重新审视了恒星形成的时间尺度和分子云的年龄问题。 人们一直认为，正在形成恒星的分子云相对于没有活跃恒星形成的云显得过多，这表明分子云是“短命”的，而恒星形成是“快速”的。 我们证明了这种统计论据缺乏一致性，甚至在快速恒星形成的情景下，也暗示云的寿命约为10百万年。 我们讨论了来自外部星系的额外观测证据，这些证据表明分子云的寿命以及恒星形成的时标大约为10百万年。 这些较长的云寿命与超音速湍流（约1百万年）的快速衰减对湍流控制恒星形成的情景提出了严重挑战。 相比之下，我们展示了31个现有观测对象的数据（线宽、大小和磁场强度已可靠测量），与双扩散理论的预测在定量上完全一致。 在双扩散控制的恒星形成理论中，线宽可以归因于大尺度非径向云振荡（本质上是驻波的大振幅长波阿尔芬波），而线宽、大小和磁场之间的预测关系是自引力云磁支持的自然结果。 显示英文摘要

摘要： We revisit the problem of the star formation timescale and the ages of molecular clouds. The apparent overabundance of star-forming molecular clouds over clouds without active star formation has been thought to indicate that molecular clouds are "short-lived" and that star formation is "rapid". We show that this statistical argument lacks self-consistency and, even within the rapid star-formation scenario, implies cloud lifetimes of approximately 10 Myr. We discuss additional observational evidence from external galaxies that indicate lifetimes of molecular clouds and a timescale of star formation of approximately 10 Myr . These long cloud lifetimes in conjunction with the rapid (approximately 1 Myr) decay of supersonic turbulence present severe difficulties for the scenario of turbulence-controlled star formation. By contrast, we show that all 31 existing observations of objects for which the linewidth, the size, and the magnetic field strength have been reliably measured are in excellent quantitative agreement with the predictions of the ambipolar-diffusion theory. Within the ambipolar-diffusion-controlled star formation theory the linewidths may be attributed to large-scale non-radial cloud oscillations (essentially standing large-amplitude, long-wavelength Alfven waves), and the predicted relation between the linewidth, the size, and the magnetic field is a natural consequence of magnetic support of self-gravitating clouds.