Observed in the IRAS Survey, Version 2, JPL
- J. F. Gallimore, S. A. Baum, O’Dea, C.P
Context. Recently, a relationship between the water maser detection rate and far infrared (FIR) flux densities has been established as a result of two 22GHz maser surveys in a complete sample of galaxies (Dec > −30) with 100μm flux densities of > 50 Jy and > 30 Jy. Aims. This survey has been extended to the southern galaxies in order to discover new maser sources and to investigate the galaxies hosting the maser spots with particular emphasis on their nuclear regions. Methods. A sample of 12 galaxies with Dec < −30 and S100 μm > 50 Jy was observed with the 70-m telescope of the Canberra Deep Space Communication Complex (CDSCC) at Tidbinbilla (Australia) in a search for water maser emission. The average 3σ noise level of the survey is 15 mJy for a 0.42 km s channel, corresponding to a detection threshold of ∼ 0.1 L⊙ for the isotropic maser luminosity at a distance of 25Mpc. Results. Two new detections are reported: a kilomaser with an isotropic luminosity LH2O ∼ 5 L⊙ in NGC3620 and a maser with about twice this luminosity in the merger system NGC3256. The detections have been followed-up through continuum and spectral line interferometric observations with the Australia Telescope Compact Array (ATCA). In NGC3256, a fraction (about a third) of the maser emission arises from two hot spots associated with star formation activity, which are offset from the galactic nuclei of the system. The remaining emission may arise from weaker centers of maser activity distributed over the central 50. For NGC3620, the water maser is coincident with the nuclear region of the galaxy. Our continuum observations indicate that the nature of the nuclear emission is most likely linked to particularly intense star formation. Including the historical detection in NGC4945, the water maser detection rate in the southern sample is 15% (3/20), consistent with the northern sample. The high rate of maser detections in the complete all-sky FIR sample (23%, 15/65) confirms the existence of a link between overall FIR flux density and maser phenomena. A relation between H2O and OH masers in the FIR sample is also discussed.