Dust and Infrared Polarization Signatures

Abstract

An outline is presented of observations and interpretations of polarization in the near and mid-infrared. Grain alignment occurs in the diffuse interstellar medium, in dense and massive molecular clouds and in HII regions as well as the boundaries of diffuse quiescent clouds; the resulting polarization displays features due to thermal excitation of molecular bonds and these are discussed in terms of grain chemistry and physics and the grain environment. In the near-infrared scattering can be a complicating factor, and at longer wavelengths polarization may be a combination of absorption and emission. Spectropolarimetry can separate these contributions and provide information on fractionation of grain material and ambient conditions along the line-of-sight. It also provides evidence on grain chemistry independent of, and more sensitive than, spectroscopy. Polarimetry also reveals magnetic field directions projected on the sky. The gains from large 10m class telescopes are particularly large in this wavelength region but not yet exploited, in spite of the availability of relevant instrumentation. Some of these will be outlined.