AST 95-27289 PI: Andrew Wilson The Masses of Supermassive Black Holes in Galactic Nuclei A few active galaxies are known to emit a luminous water vapor line at 1.3 cm wavelength through maser action. Recent studies of NGC 4258 have revealed that the masering molecules lie in a thin annulus with inner and outer radii about 0.14 and 0.28 pc, with maser emission seen from gas along the line of sight to the center of the disk and also along the "tangent points". The rotational velocity shows that the gas follows a Keplerian rotation curve with a binding mass (presumably a black hole) of 36 million solar masses. A survey of active galaxies which is about half done has already discovered nine new examples (five were known before). The survey will be completed and a statistical analysis made of the total maser sample. The new masers will be mapped with the VLA, and with VLBI for the brighter examples, and monitored for the redward drift of features seen in NGS 4258; if it is seen, it allows the centripetal acceleration, and thus the binding mass, to be measured directly. In addition, a survey of radio galaxies for water vapor emission will check theoretical prediction that very luminous water vapor maser emission exists.
