A water maser survey towards the Galactic Centre

We have used the Australia Telescope Compact Array to survey the Galactic Centre for the 22-GHz transition of water. The survey provides an unbiased search for water masers within a 0.5 deg2 region about the Centre, and the small synthesized beam directly yields positions to arcsecond accuracy. The detected sources were re-observed 4 months later and showed considerable changes in their spectra, with two sources found in the follow-up that were not seen in the original survey, yielding a total of 27 maser detections. Comparison with methanol and OH surveys shows that, at current sensitivity levels, water masers greatly outnumber the other species. 12 of our maser detections had previously been reported, discovered during searches towards interesting targets in the survey area. The majority of our sources are quite weak, consistent with excitation by young massive stars mostly near the Galactic Centre. Our spectra reveal high-velocity outflows at one-quarter of the water maser sites, a statistic similar to sites in the remainder of the Galaxy.