THE ZEEMAN EFFECT IN THE 44 GHZ CLASS I METHANOL MASER LINE TOWARD DR21(OH)

Abstract

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 H 2 O. 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 CH 3 OH transition. Data from observations of a larger number of sources are needed to make such empirical determinations robust.