AAS 203rd Meeting, January 2004
Session 63 AGN
Oral, Tuesday, January 6, 2004, 10:00-11:30am, Regency VII

## [63.09] Survey for Water Maser Emission in Active Galactic Nuclei

P. T. Kondratko, L. J. Greenhill, J. M. Moran (Harvard-Smithsonian Center for Astrophysics), J. E. J Lovell, D. L. Jauncey (Australia Telescope National Facility), T. B. Kuiper (Jet Propulsion Laboratory)

Water maser emission (\lambda=1.3 cm) traces warm dense gas in the inner parsec of accretion disks around supermassive black holes. The velocity coherence within the disk favors the detection of emission in edge-on parsec-scale disks at the systemic velocity of the host galaxy and at velocities symmetrically offset by the orbital velocity of the rotating disk. Study of water maser emission has appreciably improved our understanding of the immediate vicinity (<1 pc) of supermassive black holes. In particular, images and spectra of water maser sources have been used to: 1) measure a geometric distance to NGC 4258, 2) precisely weigh central black holes, 3) infer geometrical shapes and orientations of accretion disks, and 4) constrain accretion rates.

Surveys designed to detect water maser sources are challenging because they require both sensitive apertures and wide bandwidth, high resolution spectrometers. To discover additional water maser systems, we assembled a custom-built spectrometer with 5300 km s-1 bandwidth and have begun an all-sky survey with the NASA Deep Space Network 70-m antennas, which are among the most sensitive radio telescopes currently in operation. During the austral winters 2002 and 2003, we discovered 11 new maser sources with the 70-m antenna at Tidbinbilla. We present spectra of the newly discovered emission and preliminary statistics from the survey. Three of the newly detected sources reveal a characteristic spectral signature of an edge-on accretion disk and thus constitute particularly good candidates for the determination of accretion disk structure, black hole mass, and possibly a geometric distance.