The physics of interstellar dust in nearby galaxies

星际尘埃在星系的多相星际介质(ISM)中，在恒星的形成和反馈过程中起着至关重要的作用。尘埃颗粒是流体动力学、化学、加热、冷却和电离平衡的重要介质。尘埃通过使新形成的恒星和电离气体的光学和紫外线辐射衰减和变红，并通过在红外、远红外和亚毫米/毫米波长重新辐射吸收的辐射来塑造ISM的光谱能量分布。尽管尘埃物理很重要，但对尘埃物理的全面理解仍然受到一些开放问题的阻碍，这些问题是该项目的中心议题。(1)在亚毫米/毫米波长，在冷尘埃顶部观察到一个额外的发射分量，自由和同步辐射，特别是对低金属丰度系统的发射。人们提出了不同的理论来解释这种所谓的超额排放，但到目前为止，它的来源仍然是一个悬而未决的问题。(2)多环芳烃(PAHs)是一种高效的电荷交换中间体，在光解离区的光电加热中占主导地位，为化学反应提供了大量的表面积。多环芳烃的生命周期，即其产生、演变和破坏，还远远没有确定下来。在演化恒星的富碳大气中，在致密的分子云中，或者通过加工大颗粒，不同的主导形成机制正在争论中。(3)尘气比(DGR)与金属丰度的关系为研究尘埃演化模型和星系演化阶段提供了重要工具。然而，对于给定的金属丰度，DGR在整个金属丰度范围内表现出很大的散布，这表明金属丰度并不是DGR的唯一驱动因素，环境效应、恒星形成历史、尘埃性质和尘埃破坏效率的变化可能起到了作用。该项目的主要目标是对附近星系中的尘埃特性及其与当地ISM条件的关系进行系统的、空间分辨的分析。我们将把我们新的和存档的亚毫米/毫米地图与大量辅助多波长数据结合起来使用。我们对中性碳精细结构发射的观察将被用作分子气体的附加示踪剂，并与CO测量相结合。我们将应用数据挖掘技术中最先进的统计方法来约束复杂、多相ISM中的尘埃物理。该项目包括建立一个公开可用的数据库，并开发软件，为分析已分解的附近星系的观测情况提供统计工具，并由其他项目在优先方案框架内进行相应的模拟。

Interstellar dust plays a crucial role in the multi-phase interstellar medium (ISM) of galaxies, in star formation and feedback processes. Dust particles constitute an important agent in the fluid dynamics, chemistry, heating, cooling and ionisation balance. Dust shapes the spectral energy distribution of the ISM by attenuating and reddening the optical and ultraviolet emission of newly formed stars and ionised gas, and by re-radiating the absorbed emission at infrared, far-infrared and submm/mm wavelengths. Despite its importance, a comprehensive understanding of the dust physics is still hampered by some open issues, which denote the central topics of this project. (1) At submm/mm wavelengths an additional emission component is observed on top of the cold dust, free-free and synchrotron emission, especially towards low-metallicity systems. Different theories have been suggested to explain this so-called excess emission, but up to now its origin is an open question. (2) Polycyclic aromatic hydrocarbons (PAHs) dominate the photoelectric gas heating in photo-dissociation regions, provide large amounts of surface area for chemical reactions, and are highly efficient charge exchange intermediaries. The life cycle of PAHs, i.e. their production, evolution and destruction, is yet far from settled. Different dominant formation mechanisms in the carbon-rich atmospheres of evolved stars, in dense molecular clouds or by processing of large grains are under debate. (3) The relation between the dust-to-gas ratio (DGR) and metallicity provides an important tool to study dust evolution models and the evolutionary stage of a galaxy. Nevertheless, the DGR shows a large scatter for a given metallicity throughout the metallicity range, indicating that metallicity is not the only driver for the DGR, and that environmental effects, variations in the star formation histories, dust properties and dust destruction efficiencies may play a role. The main objective of this project is to provide a systematic, spatially resolved analysis of the dust properties in nearby galaxies, and their relation to the local ISM conditions. We will use our new and archival submm/mm maps in conjunction to the large heritage of ancillary multi-wavelength data. Our observations of the fine structure emission of neutral carbon will be used as an additional tracer of molecular gas, in conjunction to CO measurements. We will apply state-of-the-art statistical methods adapted from data mining techniques to constrain the dust physics in the complex, multi-phase ISM. The project includes the creation of a publicly available data base, and the development of software, providing statistical tools for the analysis of observations of resolved nearby galaxies and the corresponding simulations to be conducted by other projects in the framework of the Priority Program.