The Zeeman Effect in the 44 GHz Class I Methanol (CH3OH) Maser Line
  Toward DR21W
  We report the detection of the Zeeman effect in the 44 GHz Class I methanol
maser line toward the high mass star forming region DR21W. There are two
prominent maser spots in DR21W at the ends of a northwest-southeast linear
arrangement. For the maser at the northwestern end (maser A), we fit three
Gaussian components. In the strongest component, we obtain a significant Zeeman
detection, with $zB_{\rm los}=-23.4\pm3.2$ Hz. If we use $z=-0.920$ Hz
mG$^{-1}$ for the $F=5 \rightarrow 4$ hyperfine transition, this corresponds to
a magnetic field $|B_{\rm los}|=25.4$ mG; $B_{\rm los}$ would be higher if a
different hyperfine was responsible for the 44 GHz maser, but our results also
rule out some hyperfines, since fields in these regions cannot be hundreds of
mG. Class I methanol masers form in outflows where shocks compress magnetic
fields in proportion to gas density. Designating our detected $B_{\rm los}=25$
mG as the magnetic field in the post-shock gas, we find that $B_{\rm los}$ in
the pre-shock gas should be 0.1-0.8 mG. Although there are no thermal-line
Zeeman detections toward DR21W, such values are in good agreement with Zeeman
measurements in the CN thermal line of 0.36 and 0.71 mG about $3.5'$ away in
DR21(OH) in gas of comparable density to the pre-shock gas density in DR21W.
Comparison of our derived magnetic energy density to the kinetic energy density
in DR21W indicates that magnetic fields likely play a significant role in
shaping the dynamics of the post-shocked gas in DR21W.
