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

Abstract

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 ∼ 107–8 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.