Evidence for an outflow from the Seyfert galaxy NGC 4051

New observations using narrow-band imaging, long-slit spectroscopy and MERLIN observations of the nuclear region of the Seyfert galaxy NGC 4051 have been made. An edge-brightened, triangular region of ionized gas extending 420 pc from the centre of the galaxy has been detected. Long-slit spectra of this ionized gas, taken at 1.5 arcsec from the core, show the [O III]5007-A emission line to consist of two velocity components, both blueshifted from the systemic radial velocity, with velocity widths of 140 km s^^-1 and separated by 120 km s^^-1. This region is co-spatial with weak extended radio emission, and is suggestive of a centrally driven outflow. The [O III]5007-A line spectrum and image of this region are modelled as an outflowing conical structure at 50 deg to the line of sight with a half-opening angle of 23 deg. In addition to the extended structure, high-resolution MERLIN observations of the 18-cm nuclear radio emission reveal a compact (1 arcsec) radio triple source in PA 73 deg. This source is coincident with the HST-imaged emission-line structure. These high-resolution observations are consistent with a more compact origin of activity (i.e., a Seyfert nucleus) than a starburst region....