The H2O Southern Galactic Plane Survey (HOPS) - I. Techniques and H2O maser data

A. J. Walsh*, S. L. Breen, T. Britton, K. J. Brooks, M. G. Burton, M. R. Cunningham, J. A. Green, L. Harvey-Smith, L. Hindson, M. G. Hoare, B. Indermuehle, P. A. Jones, N. Lo, S. N. Longmore, V. Lowe, C. J. Phillips, C. R. Purcell, M. A. Thompson, J. S. Urquhart, M. A. VoronkovG. L. White, M. T. Whiting

*Corresponding author for this work

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152 Citations (Scopus)


We present first results of the H2O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad-band backend and a beam size of about 2 arcmin. We have observed 100 deg2 of the southern Galactic plane at 12mm (19.5-27.5GHz), including spectral line emission from H2O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H2O masers, of which 334 are new detections. The strongest maser is 3933Jy and the weakest is 0.7Jy, with 62 masers over 100Jy. In 14 maser sites, the spread in the velocity of the H2O maser emission exceeds 100kms-1. In one region, the H2O maser velocities are separated by 351.3kms-1. The rms noise levels are typically between 1 and 2Jy, with 95 per cent of the survey under 2Jy. We estimate completeness limits of 98 per cent at around 8.4Jy and 50 per cent at around 5.5Jy. We estimate that there are between 800 and 1500 H2O masers in the Galaxy that are detectable in a survey with similar completeness limits to HOPS. We report possible masers in NH3 (11,9) and (8,6) emission towards G19.61-0.23 and in the NH3 (3,3) line towards G23.33-0.30.

Original languageEnglish
Pages (from-to)1764-1821
Number of pages58
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - Sep 2011
Externally publishedYes


  • Galaxy: structure
  • ISM: molecules
  • Masers
  • Radio lines: ISM
  • Stars: formation
  • Surveys


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