DISCOVERY OF WATER MASER EMISSION IN EIGHT AGNs WITH 70 m ANTENNAS OF NASA'S DEEP SPACE NETWORK

摘要

We report the discovery of water maser emission in eight active galactic nuclei (AGNs) with the 70 m NASA Deep Space Network (DSN) antennas at Tidbinbilla, Australia, and Robledo, Spain. The positions of the newly discovered masers, measured with the VLA, are consistent with the optical positions of the host nuclei to within 1 σ (0.3″ radio and 1.3″ optical) and most likely mark the locations of the embedded central engines. The spectra of two sources, NGC 3393 and NGC 5495, display the characteristic spectral signature of emission from an edge-on accretion disk, with orbital velocities of ～600 and ～400 km s~(-1), respectively. In a survey with DSN facilities of 630 AGNs selected from the NASA Extragalactic Database, we have discovered a total of 15 water maser sources. The resulting incidence rate of maser emission among nearby (v_(sys) < 7000 km s~(-1)) Seyfert 1.8-2.0 and LINER systems is ～10% for a typical rms noise level of ～14 mJy over 1.3 km s~(-1) spectral channels. As a result of this work, the number of nearby AGNs (v_(sys) < 7000 km s(-1)) observed with < 20 mJy rms noise has increased from 130 to 449.