Red-shifted H2O emission in NGC3079:: More evidence for a pc-scale circumnuclear torus?

Using the Effelsberg 100-m telescope, sensitive measurements of the H2O megamaser in NGC3079 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 (V-LSR similar to 1120 km s(-1)). Symmetrically bracketing the systemic velocity, the H2O emission covers a velocity range of similar to 450 kms(-1) with only one potential narrow gap (similar to 20 kms (-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 NGC4258 and a complex morphology of the radio continuum leave, however, space for scepticism.