On the identification of high-mass star forming regions using IRAS: Contamination by low-mass protostars

We present the results of a survey of a small sample (14) of low-mass protostars (L-IR < 10(3) L-circle dot) for 6.7 GHz methanol maser emission performed using the ATNF Parkes radio telescope. No new masers were discovered. We find that the lower luminosity limit for maser emission is near 10(3) L-circle dot by comparison of the sources in our sample with previously detected methanol maser sources. We examine the IRAS properties of our sample and compare them with sources previously observed for methanol maser emission, almost all of which satisfy the Wood & Churchwell criterion for selecting candidate UC H-II regions. We find that about half of our sample satisfy this criterion, and in addition, almost all of this subgroup have integrated fluxes between 25 and 60 mu m that are similar to sources with detectable methanol maser emission. By identifying a number of low-mass protostars in this work and from the literature that satisfy the Wood & Churchwell criterion for candidate UC H (II) regions, we show conclusively for the first time that the fainter flux end of their sample is contaminated by lower mass nonionizing sources, confirming the suggestion by van der Walt and Ramesh & Sridharan.