Non-Zeeman Circular Polarization of Molecular Rotational Spectral Lines

Abstract

We present measurements of circular polarization from rotational spectral lines of molecular species in Orion KL, most notably 12CO (J=2 - 1), obtained at the Caltech Submillimeter Observatory with the Four-Stokes-Parameter Spectra Line Polarimeter. We find levels of polarization of up to 1 to 2% in general, for 12CO (J=2 - 1) this level is comparable to that of linear polarization also measured for that line. We present a physical model based on resonant scattering in an attempt to explain our observations. We discuss 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. We also show that the effect is proportional to the square of the magnitude of the plane of the sky component of the magnetic field, and therefore opens up the possibility of measuring this parameter from circular polarization measurements of Zeeman insensitive molecules.

30 pages, 7 figures; accepted for publication in the ApJ

References in corpus (8)

• Magnetic Fields in the Formation of Sun-Like Stars
• Magnetically Aligned Velocity Anisotropy in the Taurus Molecular Cloud
• Probing the Turbulence Dissipation Range and Magnetic Field Strengths in Molecular Clouds
• Dispersion of Magnetic Fields in Molecular Clouds. III
• The Circular Polarization of Sagittarius A* at Submillimeter Wavelengths
• Magnetic Fields and Infall Motions in NGC 1333 IRAS 4
• Submillimeter Polarization of Galactic Clouds: A Comparison of 350 micron and 850 micron Data
• Characterization of Turbulence from Submillimeter Dust Emission

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