Discovery of Three New H$_2$O Megamasers
Session 59 -- Low Luminosity AGNs and Active Galaxies
Display presentation, Thursday, 2, 1994, 9:20-6:30

## [59.13] Discovery of Three New H$_2$O Megamasers

J.A. Braatz (UMD), A.S. Wilson (STScI/UMD), C. Henkel (MPIfR)

We report observations with the MPIfR 100-meter telescope which have led to the discovery of three new H$_2$O megamasers. The observed line emission results from the 6$_{16}$ -- 5$_{23}$ rotational transition at a rest frequency of 22.235 GHz. The new masers are located in NGC 5506 (Seyfert 1.9), NGC 2639 (Seyfert 1), and Mrk 1210 (Seyfert 2), and the isotropic luminosities of the masers are 76 {\hbox{$L_{\odot}$}}, 53 {\hbox{$L_{\odot}$}}, and 84 {\hbox{$L_{\odot}$}}, respectively (H$_0$ = 75 km s$^{-1}$ Mpc$^{-1}$). The total number of extragalactic megamasers is now eight. All of them are hosted by galaxies with some level of nuclear activity, and it is likely that they ultimately derive their energy from the powerful central engine of the AGN. A number of observations offer evidence that dense nuclear gas in many Seyfert galaxies is collected in an optically and geometrically thick torus. The molecular gas in the torus is further clumped into distinct clouds, and it is possible that the megamasers originate in these clouds. The nature of the maser emission might therefore be influenced by the detailed geometry and dynamics of the torus. The megamaser sources reported here contain the most distant water yet detected in the universe.