Magnetic fields in discs : what can be learned from infrared and mm polarimetry ?

Abstract

Polarimetric imaging in the infrared and submm offers the possibility of identifying magnetic field configurations in astronomical objects. To test this conjecture a set of field geometries within internally heated discs has been modelled and polarization transfer followed for a range of view angles with respect to the disc axis. The wavelength range considered is from the mid-infrared to submm, the dominant polarization processes then being only dichroic emission and absorption by aligned grains. A sample of the resulting polarization images is presented and their salient features discussed. There are obvious, and some not so obvious, associations of polarization structure with the parent model field and, while these are not always unique, they will usually lead to strong constraints on the field configuration. For star formation regions the polarization structure is likely to be on a small spatial scale and then the full potential of this technique must await the advent of millimetre synthesis systems.