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Session 98 - AGN-Absorption/Emission.
Display session, Thursday, January 16
We have imaged the parsec--scale H_2O maser and 22 GHz continuum emission in the nucleus of the active galaxy NGC 3079 at a resolution of 1 mas using the VLBA. The brightest maser feature served as a phase reference to register the relative position of the continuum emission to an accuracy of 0.1 mas. The maser emission appears to sample a 22 mas (1.7 pc) linear structure that is approximately aligned with the major axis of the galactic disk, with a position angle of -15\deg. The positions and velocities of the features do not, however, exhibit any conspicuous pattern such as would be expected for a rotating disk. The maser emission is concentrated in three regions: one clump about 4 mas (0.3 pc) in diameter, centered on the brightest feature, that exhibits a wide range of velocities (940--1060 km s^-1); another smaller clump 7 mas to the north; and a single feature 15 mas to the south. All of the maser emission occurs at velocities blueshifted with respect to the systemic velocity of the galaxy (v_sys=1130 km s^-1) except for the single southern feature, which has a velocity of 1190 km s^-1. One 22 GHz continuum component was convincingly identified. It is compact, with a flux density of about 10 mJy, and lies 6.6 mas (0.5 pc) west of the dominant maser emission. None of the maser components is spatially coincident with the 22 GHz continuum. Hence, the extraordinary brightness of the H_2O maser emission in NGC 3079 may not result from highly beamed amplification of radiation from compact background continuum features, as has been suggested.
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Program listing for Thursday