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Scales and thresholds in molecular cloud turbulence

分子云湍流的尺度和阈值

基本信息

批准号：
203320423
负责人：
Professor Dr. Ralf Klessen, Ph.D.
金额：
--
依托单位：
Institut für Astrophysik
依托单位国家：
德国
项目类别：
Priority Programmes
财政年份：
2011
资助国家：
德国
起止时间：
2010-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/203320423?language=en
关键词：
Scales thresholds molecular cloud turbulence

项目摘要

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.

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)的模拟和最近的观测，以确定控制ISM动态演变的不同物理过程的特征尺度和参数。我们将识别和量化湍流级联特性可能发生变化的物理尺度和阈值。这些是化学混合尺度、丝状云中紫外光和红外线的典型穿透深度、特征速度模式和湍流耗散尺度。阈值由开始引力崩塌的临界密度、激发特定的线冷却过程和化学相变的临界密度给出。将尺度信息与密度、柱密度和温度统计相结合，我们将得到分子云丝的引力崩塌状态和向单个核心的转变。通过评估参数，如辐射穿透深度，逃逸概率和由此产生的冷却函数，以及不同物种之间的耦合系数，特别是中性和电离气体粒子和尘埃颗粒，我们将约束星际介质的状态方程。我们小组可获得的非常丰富的数据集，由扩展的高角度分辨率线测量(来自NANTEN2，APEX，IRAM和MOPRA望远镜)和连续数据(斯皮策，赫歇尔，普朗克成像)，使我们能够研究从恒星形成尺度到巨型分子云复合体的ISM。与此同时，我们在模拟多阶段和多尺度ISM的能力方面取得了巨大的进步，数值模拟现在不仅能够始终如一地覆盖整个星系的亚Parsec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率数据与我们小组进行的高精度数值模拟。我们的重点将放在柱密度、温度、速度和丰度等参数的概率分布函数(PDF)上，以及通过小波滤波技术检测明显的尺度，从而使我们能够在特定尺度上追踪不同物理机制对湍流叶栅的影响。利用PDF，我们检测到例如列密度阈值，其可以对应于结构形成过程的改变。小波滤波技术，如Delta-Variance和我们最近开发的互相关法，测量重要的空间尺度。我们将进一步改进这一方法，以评估细丝对ISM动力学的意义。