The physics of interstellar dust in nearby galaxies

星际尘埃在星系的多相星际介质（ISM）、星星形成和反馈过程中起着至关重要的作用。尘埃粒子构成流体动力学、化学、加热、冷却和电离平衡中的重要因素。尘埃通过衰减和红化新形成的恒星和电离气体的光学和紫外线发射，并通过在红外、远红外和亚毫米/毫米波长下重新辐射吸收的发射，塑造了ISM的光谱能量分布。尽管它的重要性，尘埃物理学的全面理解仍然受到一些开放的问题，这表明该项目的中心议题。(1)在submm/mm波长下，在冷尘埃、自由-自由和同步辐射的顶部观察到额外的发射成分，特别是对低金属含量系统。人们提出了不同的理论来解释这种所谓的过量排放，但到目前为止，它的起源是一个悬而未决的问题。(2)多环芳烃（PAHs）在光解离区的光电气体加热中占主导地位，为化学反应提供大量的表面积，并且是高效的电荷交换中间体。多环芳烃的生命周期，即其产生、演变和破坏，还远未确定。不同的主要形成机制在演化恒星的富碳大气中，在密集的分子云中或通过加工大颗粒正在争论之中。(3)尘气比（DGR）与金属丰度之间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。尽管如此，DGR显示了一个大的分散在整个金属丰度范围内的给定金属丰度，这表明金属丰度不是DGR的唯一驱动因素，环境效应，星星形成历史的变化，尘埃性质和尘埃破坏效率可能会发挥作用。该项目的主要目标是提供一个系统的，空间分辨分析的尘埃属性在附近的星系，以及它们的关系，当地的ISM条件。我们将使用我们的新的和存档的submm/mm地图结合辅助多波长数据的大遗产。我们观察到的中性碳的精细结构排放将被用作分子气体的额外示踪剂，结合CO测量。我们将应用最先进的统计方法，从数据挖掘技术，以限制在复杂的，多阶段的ISM尘埃物理。该项目包括建立一个可公开使用的数据库，开发软件，为分析已分辨的邻近星系观测结果提供统计工具，并为其他项目在优先方案框架内进行的相应模拟提供统计工具。

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.