Polarimetry in disks: How to trace magnetic fields?

Gesa Bertrang

Friday December 7th, 09:20

Magnetic fields are predicted to be an important factor for a wide range of physical processes in circumstellar disks. In the classical picture, (sub-)mm continuum polarization is the tracer for magnetic fields in disks. Aspherical dust grains, whose thermal emission is intrinsically polarized, get aligned by the magnetic field due to radiative torques. In recent years, however, this picture has been challenged. New theoretical studies show that (sub-)mm continuum polarization can also be created by scattering of the thermal dust emission or arise from aspherical grains which are aligned by the radiation field rather than the magnetic field. These three mechanisms trace fundamentally different physics in circumstellar disks, yet, their polarization predictions are not clearly distinguishable. In this talk, I will highlight the role of magnetic fields in disks, present already achieved (indirect) observational constraints, and give an outlook on how to disentangle the sources of continuum polarimetry with ALMA by applying spectro-polarimetry. Solving the present ambiguity will enable (sub-)mm polarimetry as powerful and versatile tracer of a wide range of physics.