A Subparsec Radio Jet or Disk in NGC 4151

We have imaged the classical Seyfert galaxy NGC 4151 with the VLBA at wavelengths of 6 and 18 cm, achieving resolutions of ≃2 and 5 mas (≃0.16 and 0.40 pc), respectively. At 18 cm, four radio components, spread over ≃05 (≃40 pc) are detected. The easternmost pair comprises a bright component elongated in position angle ≃20° (component E) and an extension to the northeast (component F) which curves into position angle ≃75°, similar to that of the 35 (280 pc) scale radio jet and the narrow-line region. At the higher resolution achieved at 6 cm, component E is found to be a linear radio source with a length of ~13 mas (1.0 pc). This source has a length/width ratio of ≳4, and therefore fulfills one of the classical criteria for a radio jet, but its radio luminosity is only ~1038 ergs s-1, several orders of magnitude less than the parsec-scale jets in radio galaxies. It is also misaligned by ≃55° from the arcsecond-scale radio jet. Possible reasons for the misalignment include deflection by the inner narrow-line region, buoyancy forces, and a change in the plane of the accretion disk presumably responsible for jet collimation. We also discuss an alternative interpretation, in which component E is a disk or torus viewed edge-on and emitting flat-spectrum, possibly thermal, radio emission.