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Session 56 - Active Galaxies: The Central Engine.
Oral session, Tuesday, January 16
Corte Real, Hilton
We report the first map of the water maser emission in the nucleus of the edge-on galaxy NGC 4945. This was the first water maser discovered in an AGN, though it is relatively inaccessible owing to its low declination, -49^\circ. Recent studies of water maser emission in the NGC 4258 AGN have demonstrated that masers can be very powerful probes of dynamics on subparsec scales. The nucleus of NGC 4945 is a LINER that harbors a hard X ray source. There is an ionization cone along the minor axis of the galaxy.
The maser displays two emission complexes, one close to the systemic velocity of the galaxy and one that is redshifted by about 150 km s^-1. We have measured the separation between complexes to be about 0.4 pc (15 mas at a distance of 6 Mpc), along a position angle of 45^\circ, which matches the position angle of the stellar disk and is perpendicular to the axis of the ionization cone. The maser emission in the redshifted complex consists of many Doppler components that are distributed, in projection, over about 0.03 pc. If this southern maser source arises from an edge-on Keplerian disk, as in the NGC 4258 AGN, then the binding mass is a few million M_ødot. The maser may instead be directly related to the outflow associated with the ionization cone.
