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| Paper: |
A Polarization Survey of mm Methanol Masers |
| Volume: |
343, Astronomical Polarimetry: Current Status and Future Directions |
| Page: |
160 |
| Authors: |
Wiesemeyer, H.; Thum, C.; Walmsley, C.M.; Paubert, G. |
| Abstract: |
We present a survey of the polarization properties of class I and II methanol (CH3OH) masers at mm wavelengths. Linear polarization, up to 40%, is found in more than half of the observed objects, without any clearcut distinction between both maser classes. The spectral profiles of the polarization angles are found to be either flat or have a linear slope. We conclude that the mm-line methanol masers are unsaturated, and that the strong fractional polarization is due to anisotropic pumping. In several sources, the maser polarization angles are either parallel or perpendicular to the dust continuum polarization. This suggests either the amplification of polarized background radiation by an unsaturated maser, or the same magnetic field direction for the dust and the CH3OH gas. The polarization properties of the spectrally resolved velocity components of class II methanol masers at 107 GHz and 157 GHz are quite homogeneous, which may be an indicator of velocity redistribution along a single maser axis. In two class I sources (133 GHz), circular polarization is tentatively detected, and can only be explained by conversion from linear to circular polarization. |
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