The physics of interstellar dust in nearby galaxies

• Applicant: Dr. Marcus Albrecht
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 263087833

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.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1573: Physics of the Interstellar Medium