Polarization of Class I methanol (CH3OH) masers

Abstract

AbstractMagnetic fields are known to play an important role in several stages of the star formation process. Class I methanol (CH3OH) masers offer the possibility of measuring the large-scale magnetic field in star forming regions at high angular resolution, due to connections between the large-scale magnetic field in the pre-shock regions to the observed magnetic field along the outflows in the post-shock regions where these masers are formed. The detection of the Zeeman effect in the 36 GHz and 44 GHz Class I methanol maser lines by Sarma and Momjian has opened an exciting new window into the study of the star formation process, but for the results to be interpreted correctly, the Zeeman splitting factor (z) for both these lines needs to be urgently measured by experiment. Ratios between the pre-shock and post-shock magnetic fields and densities lead to the conclusion that the value of z cannot be too different from 1 Hz mG−1, unless the predicted densities at which 36 GHz and 44 GHz methanol masers are excited are drastically incorrect. Similarities between the detected fields in 36 GHz and 44 GHz Class I masers, and 6.7 GHz Class II masers, support the claim that these masers may be tracing the large-scale magnetic field or that the magnetic field remains the same during different evolutionary stages of the star formation process, provided such similarities are not just due to the assumption of a uniform nominal value for z, or result simply from selection effects due to orientation and/or the shock process. Given the exciting possibilities, a larger statistical sample of measurements in both the 36 GHz and 44 GHz lines is certainly needed.