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Session 56 - Active Galaxies: The Central Engine.
Oral session, Tuesday, January 16
Corte Real, Hilton
In the most extensive search for extragalactic water vapor maser emission to date, we have observed a complete distance- (v< 7000 km s^-1) and magnitude-limited (m_b < 14) sample of AGN. We have discovered 9 new masers, making 14 known sources with isotropic luminosities > 30 L(sun). VLA observations confirm that the maser sources are compact and are located near the galactic nuclei. Though the tally of these masers is still small, we have begun to apply statistical analysis techniques. All of the masers are found in the nuclei of Seyfert 2 or LINER galaxies -- none in Seyfert 1's. Such a distribution suggests that the masers are beamed in the plane of the nuclear molecular torus hypothesized by unified theories of AGN.
Monitoring observations of the water masers show, in certain cases, that the velocities of individual maser components drift systematically redward with time. Such velocity drifts probably trace the centripetal acceleration of the maser clouds due to the central mass in the AGN. With an independent measurement of the velocity of these clouds (which is given, for example, by ``satellite'' emission lines) or of their distance from the nuclear mass, we can calculate the mass of the central object.
Velocity changes are also detected in the remarkable broad water emission feature in NGC 1052. We will discuss alternative physical conditions which might account for the unusual emission in this source. NGC 1052 is the only elliptical galaxy among those with detected masers, and the only one with a strong 22 GHz nuclear continuum.
