Methanol radio emission at millimeter wavelengths: New masers at 1.3 and 2.8 millimeters

The results of a search for maser emission in the methanol lines 8 −1 -7 0 E at 229.8 GHz, 3 −2 -4 −1 E at 230.0 GHz, 0 0 -1 −1 E at 108.9 GHz, and in the J 1 - J 0 E series near 165 GHz in star-forming regions are reported. At least two masers and two candidates have been detected at 229.8 GHz. Thus, methanol masers have been detected in the 1-mm band for the first time. At 108.9 GHz, masers have been detected toward G345.01+1.79 and possibly toward M8E as well. Thermal emission was found toward 28 objects. The 229.8-GHz sources are class I masers, whereas the 108.9-GHz sources are class II masers. An analysis using a large velocity-gradient method shows that the 229.8-GHz masers can appear at densities of about 3×10 4 cm −3 . The ratios of the flux densities in different class I lines toward DR 21(OH) and DR 21 West can be approximated in models with gas kinetic temperatures of about 50 K. Detection of the 108.9 GHz masers toward G345.01+1.79 and M8E may provide information about the geometry of these objects.