First Interferometric Images of the 36 GHz Methanol Masers in the DR21 Complex

TL;DR

This paper presents the first interferometric images of 36 GHz methanol masers in the DR21 complex, revealing their spatial distribution, association with other maser types, and magnetic field signatures, advancing understanding of star-forming environments.

Contribution

It provides the first high-resolution interferometric imaging of 36 GHz methanol masers and analyzes their spatial and magnetic properties in the DR21 star-forming region.

Findings

36 GHz masers are spatially overlapping with other class I masers.

Detection of Zeeman signature suggests strong magnetic fields or alternative interpretations.

Diverse maser phenomena indicate varying physical conditions in the region.

Abstract

Class I methanol masers are believed to be produced in the shock-excited environment around star-forming regions. Many authors have argued that the appearance of various subsets of class I masers may be indicative of specific evolutionary stages of star formation or excitation conditions. Until recently, however, no major interferometer was capable of imaging the important 36 GHz transition. We report on Expanded Very Large Array observations of the 36 GHz methanol masers and Submillimeter Array observations of the 229 GHz methanol masers in DR21(OH), DR21N, and DR21W. The distribution of 36 GHz masers in the outflow of DR21(OH) is similar to that of the other class I methanol transitions, with numerous multitransition spatial overlaps. At the site of the main continuum source in DR21(OH), class I masers at 36 and 229 GHz are found in virtual overlap with class II 6.7 GHz masers. To the south of the outflow, the 36 GHz masers are scattered over a large region but usually do not appear coincident with 44 GHz masers. In DR21W we detect an "S-curve" signature in Stokes V that implies a large value of the magnetic field strength if interpreted as due to Zeeman splitting, suggesting either that class I masers may exist at higher densities than previously believed or that the direct Zeeman interpretation of S-curve Stokes V profiles in class I masers may be incorrect. We find a diverse variety of different maser phenomena in these sources, suggestive of differing physical conditions among them.