Scales and thresholds in molecular cloud turbulence

我们建议利用在第一个应用阶段开发和研究的统计工具，系统地比较湍流多相星际介质（ISM）的模拟。与最近的观察，以确定特征尺度和参数，支配不同的物理过程，支配ISM的动态演变。我们将确定和量化的物理尺度和阈值，其中的湍流级联的属性预计会有所改变。这些是化学混合尺度，紫外线和红外线在对流云中的典型穿透深度，特征速度模式和湍流耗散尺度。例如，由临界密度为引力坍缩的开始，为特定的线冷却过程的激发，和为化学相变。结合尺度信息与密度、柱密度和温度统计，我们将导出分子云细丝中的引力坍缩状态和向单个核的过渡。通过评估辐射穿透深度、逃逸概率和由此产生的冷却函数等参数，以及不同物质之间的耦合系数，特别是中性和电离气体粒子和尘埃颗粒之间的耦合系数，我们将约束星际介质的状态方程。（来自NANTEN2，APEX，IRAM和MOPRA望远镜）和连续数据（Spitzer，Herschel，Planck成像），使我们能够研究ISM从恒星形成尺度到巨型分子云复合体的尺寸。与此同时，我们对多相和多尺度ISM的建模能力也取得了巨大的进步，数值模拟现在不仅能够始终覆盖整个星系的亚秒差距尺度，而且还开始包括辐射传输和化学网络。结合这两条研究路线，我们将比较高分辨率多频数据与我们小组进行的高精度数值模拟。我们的重点将在于概率分布函数（PDF）的参数，如柱密度，温度，速度，和丰度，并通过小波滤波技术，使我们能够跟踪的痕迹，在特定尺度上的湍流级联的不同物理机制的检测明显的尺度。对于我们检测到的PDF，例如，列密度阈值，其可对应于结构形成工艺的改变。小波滤波技术，如三角洲方差和我们最近开发的互相关方法测量显着的空间尺度。我们将进一步改进这种方法，以评估的重要性，丝ISM动力学。

We propose to exploit the statistical tools developed and investigated in the first application period to systematically compare simulations of the turbulent multi-phase interstellar medium (ISM) with recent observations in order to identify characteristic scales and parameters governing the different physical processes that govern the dynamic evolution of the ISM.We will identify and quantify physical scales and thresholds where the properties of the turbulent cascade are expected to change. These are chemical mixing scales, the typical depth of UV and IR penetration in filamentary clouds, characteristic velocity patterns, and turbulence dissipation scales. Thresholds are given, e.g., by the critical density for the onset of gravitational collapse, for the excitation of particular line cooling processes, and for chemical phase transitions. Combining the scale information with the density, column density and temperature statistics, we will derive the state of the gravitational collapse in molecular cloud filaments and the transition to individual cores. By evaluating parameters such as radiation penetration depths, escape probabilities and the resulting cooling functions, as well as coupling coefficients between different species, in particular neutral and ionized gas particles and dust grains, we will constrain the equation of state of the interstellar medium.The very rich data sets available to our group, provided by extended, high angular resolution line surveys (from the NANTEN2, APEX, IRAM, and MOPRA telescopes) and continuum data (Spitzer, Herschel, Planck imaging), allow us to investigate the ISM from star-forming scales up to the dimension of giant molecular cloud complexes. At the same time, there has been tremendous progress in our capabilities of modeling the multi-phase and multi-scale ISM, with numerical simulations now capable not only to consistently cover subparsec scales up to full galaxies, but also start to include radiative transfer and chemical networks. Combining both lines of research, we will compare high-resolution multi-frequency data with high-precision numerical simulations performed in our group. Our focus will lie on probability distribution functions (PDF) of parameters such as column density, temperature, velocity, and abundances, and on the detection of pronounced scales through wavelet filtering techniques that allow us to trace the imprint of the different physical mechanisms on the turbulent cascade at particular scales. With the PDFs we detect, e.g., column density tresholds, that may correspond to a change of the structure forming processes. Wavelet filtering techniques, like the Delta-variance and our recently developed cross-correlation method measure significant spatial scales. We will further improve this approach in order to assess the significance of filaments for ISM dynamics.