New H2O masers in Seyfert and FIR bright galaxies. III. The Southern Sample

Recently, a relationship between the water maser detection rate and far infrared (FIR) flux densities has been established as a result of two 22 GHz maser surveys in a complete sample of galaxies (Dec>-30 degree) with 100 micron flux densities of > 50 Jy and > 30 Jy. 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. A sample of 12 galaxies with Dec<-30 degree and S(100 micron)>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 3 sigma noise level of the survey is 15 mJy for a 0.42 km/s channel, corresponding to a detection threshold of ~0.1 solar luminosities for the isotropic maser luminosity at a distance of 25 Mpc. Two new detections are reported: a kilomaser with an isotropic luminosity L_H2O ~5 solar luminosities 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 arcsec. [abridged]