SIMBAD references

Using the Green Bank Telescope, we have conducted a survey for 1.3 cm water maser emission toward the nuclei of nearby active galaxies, the most sensitive large survey for H₂O masers to date. Among 145 galaxies observed, maser emission was newly detected in 11 sources and confirmed in one other. Our survey targeted nearby (v<12,000 km/s), mainly type 2 active galactic nuclei (AGNs) north of δ=-20° and includes a few additional sources as well. We find that more than one-third of Seyfert 2 galaxies have strong maser emission, although the detection rate declines beyond v∼5000 km/s because of sensitivity limits. Two of the masers discovered during this survey are found in unexpected hosts: NGC 4151 (Seyfert 1.5) and NGC 2782 (starburst). We discuss the possible relations between the large X-ray column to NGC 4151 and a possible hidden AGN in NGC 2782 to the detected masers. Four of the masers discovered here, NGC 591, NGC 4388, NGC 5728, and NGC 6323, have high-velocity lines symmetrically spaced about the systemic velocity, a likely signature of molecular gas in a nuclear accretion disk. The maser source in NGC 6323, in particular, reveals the classic spectrum of a ``disk maser'' represented by three distinct groups of Doppler components. Future single-dish and VLBI observations of these four galaxies could provide a measurement of the distance to each galaxy and of the Hubble constant, independent of standard candle calibrations.