Laboratory measurements of the far-infrared to millimeter dust opacity at low temperatures

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The thermal emission of cold dust in the far infrared up to the millimeter range is an important source of information for studies of the spatial distribution of the interstellar medium. The interpretation of observations in this spectral range, as they were or are performed with Herschel, Planck, and ALMA, depends on the exact knowledge of the emission properties of the dust particles, i.e. the dust opacity. The available opacity data, however, are based on relatively few laboratory measurements for some selected materials only and on a still quite poor understanding of the underlying physical effects. Although the strong influence of temperature on the sub-millimeter opacity is known in principle, so far only a few measurements at low temperatures have been carried out. The aim of the project is to broaden this data base by laboratory measurements on important interstellar-dust materials such as amorphous silicates of different iron content (phase I), carbonaceous materials (phase II), and for mixtures e.g. of silicate, ice and carbon- or iron-based materials. The influence of temperature, of inhomogeneous compositions and of particle agglomeration on the opacity will be investigated in detail. Understanding the physical interrelations and improving the astrophysical dust models requires measurements in a wide wavelength range, which we achieve by combining experiences and devices from two institutes (Jena and Cologne).