New H2O masers associated with far-infrared sources

Abstract

H2O masers have been searched for in the direction of far-infrared sources found in a recent survey. There are 25 H2O masers near the 42 far-IR sources, of which 13 masers are new detections. Many of the far-IR sources are in the general vicinity of compact H II regions, and are thus likely to be young objects. Results are consistent with a 50-100 per cent coincidence of H2O masers with far-IR sources, suggesting that such objects are even more suitable candidates for maser searches than the compact H II regions. The high coincidence rate implies a lifetime of more than 2 x 10 to the 5th years for the maser phase. The large velocity differences between the H2O features and the molecular clouds in the directions of these sources are similar to those observed in the more well-known H2O sources studied by VLBI. As in those sources, the velocities imply mass loss. Hence the far-IR sources are probably not 'protostars' in a phase of pure contraction.