The Role of the Multi-Phase Interstellar Medium in Star Formation: From Clouds to Galaxies

位于紫金山天文台（PMO）、海德堡大学天文学中心（ZAH）和海德堡马克斯-普朗克天文学研究所（MPIA）的研究小组之间的合作将描述恒星形成的物理条件、分子气体及其与恒星形成过程的关系，利用新的、全面的数据集来定义该领域最先进的技术。在其他星系中，这种气体的物理条件仍然很少受到限制，但它们在调节星系中恒星形成的效率方面发挥着关键作用。这个中德联合科学项目将通过双管齐下的方法来解决这个关键问题：(1)通过在附近星系的大样本中利用两个新的（亚）毫米成像调查密集分子气体示踪剂；“麻辣烫”（目前正在JCMT单碟望远镜上进行，由中国团队领导）和“帝国”（观测完成，数据已准备好）；(2)通过对附近形成恒星的螺旋星系NGC6946内部单个分子云尺度上分子气体物理条件的详细、高分辨率案例研究。我们空前丰富的数据集包含了由VLA和PdBI干涉仪观测到的从~10到1mm波长的20多个分子跃迁，为全面模拟物理条件和探索它们在云尺度上调节恒星形成的各自作用打开了大门。直接的科学目标是(a)开发一个由各种分子气体示踪剂在云尺度上探测的物理条件的一般模型，(b)校准这些转换中的单个（或少数组合），以便在更广泛的河外环境中使用(c)约束高密度、在云和星系尺度上立即形成恒星的物质和(d)利用这些信息来研究致密分子气体-恒星形成的关系，相对于目前青睐的恒星形成理论，(e)推导出更精确的光度，分子气体质量转换因子作为物理条件的函数(f)对星系冲击的化学示踪剂进行基准测试(g)为附近星系建立一个密度敏感分子转变的大型数据库。在三年的资助期内，我们将在这些研究成果的基础上，进一步共同制定一系列下一代观测建议，重点关注NOEMA和ALMA，特别是考虑到中国未来对前者设施的参与。拟议的项目建立在长期合作的基础上，远远超出了资助期。所要求的资金将使我们能够合并所有三个小组关于河外ISM研究的强大专业知识，为高影响力的结果提供强大的基础。这笔赠款将启动这一合作，并使中国和德国的所有小组成员能够频繁和密切地互动。

The collaboration between research groups located at the Purple Mountain Observatory (PMO), the Center for Astronomy at the University of Heidelberg (ZAH) and the Max-Planck Institute for Astronomy (MPIA) in Heidelberg will characterise the physical conditions of the star forming, molecular gas and their relation to the star formation process exploiting new, comprehensive data sets defining the state-of-the-art in the field. The physical conditions of this gas remain poorly constrained in other galaxies, yet they play the key role regulating the efficiency of star formation in galaxies. This joint Chinese-German science program will address this key question via a two-pronged approach: (1) via utilising two new (sub)millimeter imaging surveys of dense molecular gas tracers in a large sample of nearby galaxies: MALATANG (currently underway at the JCMT single dish telescope and led by the Chinese group) and EMPIRE (observations finished and data are science ready) and (2) via a detailed, high-resolution case study of the physical conditions in the molecular gas on scales of individual molecular clouds in the inner part of the nearby star-forming spiral galaxy NGC6946. Our unprecedentedly rich dataset containing more than 20 molecular transitions observed from ~10 to 1mm wavelength by the VLA and PdBI interferometers opens the door for comprehensive modelling of the physical conditions and probing their respective role in regulating star formation on cloud scales. The immediate science goals are (a) to develop a general model of the physical conditions probed by various molecular gas tracers on cloud-scales, (b) calibrate individual (or combination of very few) of these transitions to be used in a wider extragalactic context (c) to constrain the physical conditions of the high-density, imminently star forming material on cloud and galaxy scales and (d) use this information to investigate the dense molecular gas-star formation relation with respect to currently favoured theories of star formation, (e) derive more accurate luminosity to molecular gas mass conversion factors as a function of physical conditions (f) to benchmark chemical tracers for galactic shocks and (g) to build a large database of density sensitive molecular transitions for nearby galaxies. During the 3 years of this grant, we will further jointly develop a series of next generation observing proposals directly building on the results from these studies, with a focus on NOEMA and ALMA, in particular in light of China's future involvement in the former facility. The proposed project is set up with a long-term collaboration in mind, extending significantly beyond the funding period. The requested funding will allow us to merge the strong expertise regarding extragalactic ISM studies in all 3 groups, providing a powerful basis for high-impact results. This grant will jump-start this collaboration and enable frequent and close interaction of all group members in China and Germany.