STATISTICAL PROPERTIES OF 12.2 GHz METHANOL MASERS ASSOCIATED WITH A COMPLETE SAMPLE OF 6.7 GHz METHANOL MASERS

Abstract

We present definitive detection statistics for 12.2 GHz methanol masers toward a complete sample of 6.7 GHzmethanol masers detected in the Methanol Multibeam survey south of declination −20◦. In total, we detect 25012.2 GHz methanol masers toward 580 6.7 GHz methanol masers. This equates to a detection rate of 43.1%, whichis lower than that of previous significant searches of comparable sensitivity. Both the velocity ranges and the fluxdensities of the target 6.7 GHz sources surpass that of their 12.2 GHz companion in almost all cases. Eighty percentof the detected 12.2 GHz methanol maser peaks are coincident in velocity with the 6.7 GHz maser peak. Our datasupport an evolutionary scenario whereby the 12.2 GHz sources are associated with a somewhat later evolutionarystage than the 6.7 GHz sources devoid of this transition. Furthermore, we find that the 6.7 GHz and 12.2 GHzmethanol sources increase in luminosity as they evolve. In addition to this, evidence for an increase in velocity rangewith evolution is presented. This implies that it is not only the luminosity but also the volume of gas conduciveto the different maser transitions that increases as the sources evolve. Comparison with GLIMPSE mid-infraredsources has revealed a coincidence rate between the locations of the 6.7 GHz methanol masers and GLIMPSEpoint sources similar to that achieved in previous studies. Overall, the properties of the GLIMPSE sources withand without 12.2 GHz counterparts are similar. There is a higher 12.2 GHz detection rate toward those 6.7 GHzmethanol masers that are coincident with extended green objects.