2017ApJ...834..168M

We report detection of the Zeeman effect in the 44 GHz Class I methanol maser line, toward the star-forming region DR21(OH). In a 219 Jy beam^–1 maser centered at an LSR velocity of 0.83 km s^–1, we find a 20-σ detection of zB_los = 53.5 ± 2.7 Hz. If 44 GHz methanol masers are excited at n ∼ 10^7–8 cm^–3, then the B versus n^1/2 relation would imply, from comparison with Zeeman effect detections in the CN(1 - 0) line toward DR21(OH), that magnetic fields traced by 44 GHz methanol masers in DR21(OH) should be ∼10 mG. Combined with our detected zB_los = 53.5 Hz, this would imply that the value of the 44 GHz methanol Zeeman splitting factor z is ∼5 Hz mG^–1. Such small values of z would not be a surprise, as the methanol molecule is non-paramagnetic, like H₂O. Empirical attempts to determine z, as demonstrated, are important because there currently are no laboratory measurements or theoretically calculated values of z for the 44 GHz CH₃OH transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.