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On the occurrence of the 6.7 GHz CH3OH maser emission in UCH II regions
C. Codella 1,2 and
L. Moscadelli 3
Received 21 April 2000 / Accepted 30 August 2000
We present the results of a statistical survey of the 6.7 GHz CH3OH and 22.2 GHz H2O emissions towards a large homogeneous sample of ultracompact (UC) H II regions, performed to investigate the nature of the methanol emission: does it point out ionized regions or does it trace earlier stages of the star forming process?
The present detection rates are almost identical: 23% for CH3OH and 22% for H2O. Even considered the uncertainties of the survey, the large number of non-detections is consistent with the scenario where methanol masers disappear during the UC phase, like water masers do. Moreover, the probability to have the CH3OH counterpart of a H2O source is at least 40%, indicating that these maser emissions are emphasizing two at least partly overlapping evolutionary phases. The comparison between the velocity ranges suggests that methanol and water masers form in different gas components related to the star forming process.
Key words: ISM: clouds ISM: H ii regions ISM: molecules radio lines: ISM
Send offprint requests to: C. Codella (firstname.lastname@example.org)
Online publication: October 24, 2000