Resolved spectroscopy of the narrow-line region in NGC 1068: Kinematics ofthe ionized gas

We have determined the radial velocities of the [O III]-emitting gas in the inner narrow-line region of the Seyfert 2 galaxy NGC 1068, along a slit at position angle 202 degrees, from STIS observations at a spatial resolution of 0."1 and a spectral resolving power of lambda/Delta lambda approximate to 1000. We use these data to investigate the kinematics of the narrow-line region within 6" (similar to 430 pc) of the nucleus. The emission-line kno ts show evidence for radial acceleration to a projected angular distance of 1."7 in most cases, followed by deceleration that approaches the systemic velocity at a projected distance of similar to 4". We find that a simple ki nematic model of biconical radial outflow can match the general trend of ob served radial velocities. In this model, the emitting material is evacuated along the bicone axis, and the axis is inclined 5 degrees out of the plane of the sky. The acceleration of the emission-line clouds provides support for dynamical models that invoke radiation and/or wind pressure. We suggest that the deceleration of the clouds is due to their collision with a patch y and anistropically distributed ambient medium.