SIMULTANEOUS OBSERVATIONS OF H 2 O AND SIO MASERS TOWARD KNOWN EXTRAGALACTIC WATER MASER SOURCES

We observe ten known 22GHz H₂O maser galaxies during February 19–22, 2011 using the 21 m Tamna telescope of the Korean VLBI Network and a new wide-band digital spectrometer. Simultaneously we searched for 43GHz SiO v = 1, 2, J = 1–0 maser emission. We detect H₂O maser emission towards five sources (M 33, NGC 1052, NGC 1068, NGC 4258, M 82), with non-detections towards the remaining sources (UGC 3193, UGC 3789, Antennae H₂O-West, M 51, NGC 6323) likely due to sensitivity. Our 22GHz spectra are consistent with earlier findings. Our simultaneous 43GHz SiO maser search produced non-detections, yielding – for the first time – upper limits on the 43GHz SiO maser emission in these sources at a 3 σ sensitivity level of 0.018K–0.033K (0.24 Jy–0.44 Jy) in a 1.75 km s −1 velocity resolution. Our findings suggest that any 43GHz SiO masers in these sources (some having starburst-associated H₂O kilomasers) must be faint compared to the 22GHz H₂O maser emission.