Martin HoudeWestern Science

Non-Zeeman Circular Polarization of Molecular Spectral Lines

Using the Four-Stokes-Parameter Spectral Line Polarimeter (FSPPol) developed in my laboratory at the Caltech Submillimeter Observatory we successfully detected the presence of non-Zeeman circular polarization signals in molecular rotational spectral lines (e.g., CO (J = 2 → 1) in Orion KL (Houde et al. 2013, ApJ, 764, 24). We were successful in explaining these unexpected results through the conversion of linear polarization to circular polarization stemming from a novel physical process. This process, anisotropic resonant scattering, describes how slight differences in scattering amplitudes for radiation polarized parallel and perpendicular to the ambient magnetic field, responsible for the alignment of the scattering molecules, can lead to the observed circular polarization. These results have also recently been observed in a different object (supernova remnant IC 443) using the IRAM 30m telescope (Hezareh et al. 2013, A&A, submitted).


Dust Polarization Map of IC 443-G

Fig. 4. Dust polarization map of IC 443-G at 345 GHz with half-beam sampling obtained with PolKa at the APEX telescope. The polarization level is up to 10% and the magnetic field is oriented perpindicular to the long axis of the source. All the plotted polarization vectors have p ≥ 3σp. The beam size is shown in the lower right corner.

Supernova Remnant IC 443

Fig. 5†. Supernova remnant IC 443, located within the constellation Gemini at a distance of approximately 5,000 light years from Earth. 
†[Image produced by NASA and used under public domain.]