The Structured Interstellar Medium: Infrared-dark clouds from Herschel to ALMA

分子气体是星际介质(ISM)中体积分数最小的物质，但它在恒星的形成过程中起着至关重要的作用。分子云中最密集的凝聚限于银河系平面上的丝状结构；其中最引人注目的结构是红外暗云(IRDC)，它们位于旋臂上，分子气体在银河系中的分布达到顶峰。红外星云被认为是丰富星团的诞生地。由于来自嵌入的原恒星的光被尘埃严重遮挡，所以红外直流星团中恒星的形成受到的限制很小。赫歇尔现在第一次提供了对远红外的高分辨率访问，在那里尘埃的消光减少了。这一提议旨在将赫歇尔看到的小结构与大尺度的细丝联系起来，以便利用赫歇尔、斯皮策和对研究良好的IRDC样本的毫米(线和连续)观测，了解IRDC碎裂并最终形成恒星的条件。我们还将使用Platform de Bure干涉仪和ALMA对高分辨率分子线图进行调查，这将有助于限制IRDC在碎裂的不同阶段的运动学。这套观测将测试使用辐射传输建模的分子云模拟的预测。通过对IRDC模型提供强大的观测约束，该项目为形成ISM最密集阶段的相干模型奠定了基础。

Molecular gas makes up the smallest volume fraction of the phases of the interstellar medium (ISM), yet it is of paramount importance in the formation of stars. The densest condensations in molecular clouds are confined to filamentary structures in the Galactic plane; the most striking of these structures are infrared-dark clouds (IRDCs), which reside in the spiral arms where the molecular gas distribution in the Milky Way peaks. IRDCs are thought to be the birthplaces of rich star clusters. Star formation in IRDCs is poorly constrained because light from embedded protostars is heavily obscured by dust. For the first time, Herschel now provides high-resolution access to the far-infrared, where the extinction by dust lessens. This proposal aims to connect the small structures seen by Herschel to large-scale filaments in order to understand the conditions under which IRDCs fragment and ultimately form stars using Herschel, Spitzer, and millimeter (line and continuum) observations of a well-studied sample of IRDCs. We will also conduct a survey of high-resolution molecular line maps using the Plateau de Bure Interferometer and ALMA that will help constrain the kinematics in IRDCs at various stages of their fragmentation. This suite of observations will test predictions of molecular cloud simulations using radiative transfer modeling. By providing powerful observational constraints on models of IRDCs, this project serves as a bedrock for forming a coherent model of the densest phase of the ISM.