H 2 O emission in NGC 3079 : More evidence for a pc - scale circumnuclear torus ? ⋆

Using the Effelsberg 100-m telescope, sensitive measurements of the H2O megamaser in NGC 3079 are presented. During 2000 – 2001, 'high velocity' features are seen that are red-shifted up to 225 km s −1 with respect to the systemic velocity of the galaxy (VLSR ∼ 1120 km s −1). Symmetrically bracketing the systemic velocity, the H2O emission covers a velocity range of ∼450 km s −1 with only one potential narrow gap (∼20 km s −1) near the systemic velocity itself. Velocity drifts of individual components are not convincingly detected. It is shown that the presence of red-shifted emission and the absence of detectable velocity drifts are not inconsistent with the existence of a rotating circumnuclear maser disk at the very center of the galaxy. Significant differences in the overall line profile compared to NGC 4258 and a complex morphology of the radio continuum leave, however, space for scepticism.