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On the selection of ultra-compact HII regions from the IRAS Point Source Catalogue: What the 6.7-GHz methanol maser surveys tell us
D.J. van der Walt
Received 1 October 1996 / Accepted 18 November 1996
The detection rate of 6.7-GHz methanol masers in IRAS based surveys is discussed within the framework of a model for the distribution and far-infrared characteristics of embedded ionizing stars in the Galaxy. It is shown that the fainter IRAS sources selected with the Wood & Churchwell (1989) criteria have a distribution in Galactic latitude that is completely different from what is expected for embedded ionizing stars. It is concluded that a significant fraction of the fainter sources selected with the Wood & Churchwell criteria are most probably not embedded ionizing stars. The model also predicts that a significant fraction of embedded ionizing stars, primarily the less massive ones, are not expected to be exceptionally bright in the far-infrared and are also expected to be located at very small Galactic latitudes.
Key words: masers Hii regions ISM: clouds radio lines: ISM
Send offprint requests to: D.J. van der Walt
Online publication: June 30, 1998