Masers as signposts of high-mass protostars

A water maser survey of methanol maser sources

¹ Toruń Centre for Astronomy, Nicolaus Copernicus University, Gagarina 11, 87100 Toruń, Poland e-mail: msz@astro.uni.torun.pl
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 26 November 2004
Accepted: 31 December 2004

Abstract

The 22 GHz H₂O maser line was observed towards 79 candidate high-mass protostellar objects from a flux-limited sample of 6.7 GHz methanol sources. The emission was detected in 41 sources, towards 28 of these for the first time. The detection rate of 52% was similar to rates reported for other samples of high-mass protostars selected mainly with far-infrared (FIR) colour criteria. The median value of H₂O maser luminosity of is equal to that of the CH₃OH maser luminosity, whereas the median OH maser luminosity was found to be ~1.5 orders of magnitude lower. Comparison of the velocity ranges showing maser emission implies that for the majority of sources the H₂O and CH₃OH maser lines originate from different regions. The percentage of sources with emission in two or three of the maser species, their association with radio continuum and IR emission and the maser and IR luminosities are consistent with the view that evolutionary phases with H₂O and CH₃OH masers largely overlap and precede the OH maser phase, while at a later stage OH and CH₃OH masers may coexist. Strong correlations of OH and CH₃OH maser luminosities with IR luminosity and only a marginal correlation of H₂O and IR luminosity confirm current pumping schemes of all three maser lines.