The Zeeman Effect in the 44 GHz Class I Methanol (CH3OH) Maser Line Toward DR21W

Abstract

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 $z{B}_{\mathrm{los}}=-23.4\pm 3.2$ Hz. If we use $z=-0.920$ Hz mG${}^{-1}$ for the $F=5\to 4$ hyperfine transition, this corresponds to a magnetic field $|B_{\mathrm{los}}|=25.4$ mG; $B_{\mathrm{los}}$ 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 $B_{\mathrm{los}}=25$ mG as the magnetic field in the post-shock gas, we find that $B_{\mathrm{los}}$ 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 $3.5^{\prime }$ 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.

8 pages, 5 figures, ApJ accepted

References in corpus (5)

• WFCAM, Spitzer-IRAC and SCUBA observations of the massive star forming region DR21/W75: I. The collimated molecular jets
• The cooling of atomic and molecular gas in DR21
• Linear Polarization of Class I Methanol Masers in Massive Star-Forming Regions
• The Zeeman Effect in the 44 GHz Class I Methanol Maser Line toward DR21(OH)
• Non-Zeeman Circular Polarization of Molecular Maser Spectral Lines

Cited by in corpus (2)

• A Curious Case of Circular Polarization in the 25 GHz Methanol Maser Line toward OMC-1
• Polarization properties of methanol masers