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D. Sand (NRAO/UCLA), J. Braatz (NRAO), L. Greenhill (CfA)
Extragalactic water masers are excellent tools for studying the central regions of active galactic nuclei. VLBI observations have shown that water maser emission is associated with thin, parsec-scale molecular disks located near the spout of radio continuum jets. In order to study this general model, the fifteen water maser emitting galaxies observable by the VLA were imaged in A-array in April 1998. Two IFs were used simultaneously, one tuned to the frequency of the maser emission and the other slightly offset in order to gauge the continuum emission without any low level maser contamination. Both line and continuum data were successfully imaged for six of the sources, while for one other only the continuum data was successfully imaged. The remaining seven sources were not detected, due to instrumental or atmospheric instabilities. Of the sources with both line and continuum detections, three (NGC 3079, NGC 1052, and IC 1481) had measurable separations between the maser and continuum emission peaks and three (NGC 4258, NGC 1068, and NGC 2639) had maser and continuum emission coincident to within the observational uncertainties (roughly 1 pc for each). NGC 3079 and NGC 1052 both show projected separations of about 0.3 pc, which is in agreement with previous VLBI studies. IC 1481 has a much larger projected separation of 5.4 pc. If the maser geometry in IC 1481 is similar to that in NGC 4258, it would imply a central black hole mass of 1.7 x 107 solar masses.