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

分子气体在星际介质（ISM）中所占的体积分数最小，但在恒星的形成中却起着至关重要的作用。分子云中密度最大的凝聚仅限于银道面的丝状结构；这些结构中最引人注目的是红外暗云（irdc），它位于银河系分子气体分布最密集的螺旋臂中。irdc被认为是富星团的诞生地。irdc中的恒星形成受到的约束很差，因为来自嵌入的原恒星的光被尘埃严重遮挡。现在，赫歇尔首次提供了高分辨率的远红外波段，在那里尘埃的消失减少了。这个提议的目的是将赫歇尔看到的小结构与大尺度细丝联系起来，以便利用赫歇尔、斯皮策和毫米（线和连续体）对一个研究得很好的irdc样本的观测，了解irdc分裂并最终形成恒星的条件。我们还将使用高原de Bure干涉仪和ALMA进行高分辨率分子线形图的调查，这将有助于限制irdc在其碎片化的各个阶段的运动学。这组观测结果将检验利用辐射传输模型对分子云模拟的预测。通过对irdc模型提供强大的观测约束，该项目为形成ISM最密集阶段的连贯模型奠定了基础。

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.