The Parkes survey of methanol masers at 44.07 GHz

A survey of the Class I methanol masers in the transition |7₀-6₁ \ A⁺| at 44.07 GHz has been carried out with the Parkes radio telescope. About 250 positions were searched in the direction of Galactic H II regions, |H₂ O| masers and 6.7-GHz Class II methanol masers. 55 new methanol emission sources at 44 GHz were detected, amongst which is the second strongest in the sky, M8E, with a flux density of 520 Jy. Most of the newly found sources are associated with |H₂ O|⁠, OH and 6.7-GHz methanol masers and presumably are located in the common regions of star formation. A strong anticorrelation between Class I and II methanol masers was discovered. The nature of the anticorrelation is such that strong Class I masers do not co-exist with strong Class II masers and, where Class I and II masers co-exist, they have different radial velocities. The anticorrelation may be a consequence of the pumping radiation field acting on the population inversion, which is different for the two classes of masers. We suggest that the definitions of Class I and II methanol masers should be based solely on their transitions, and not by relating them to a particular type of associated astronomical object, as was originally proposed by Batrla et al. and Menten.