  We have used high resolution longslit spectroscopy to investigate the ionized
gas in the active galaxy IRAS 04210+0400 and its association with the radio
structure.
  We suggest that two of the ionized components are associated with the central
double radio source and observe that the relative positions of these components
vary for different emission lines. Both results are consistent with the radio
components representing the working surfaces of a pair of jets emerging from
the centre of the galaxy. In this scenario, the optical emission in the centre
arises behind the bowshocks produced by the jets in the interstellar medium.
  The emission lines are detected and show a dramatic (~ 900 km/s) spread in
velocity at the position of the radio lobe hotspots. We suggest a model which
explains this phenomenon as the result of a jet head emerging through the
boundary between the interstellar and intergalactic medium. A similar scenario
has previously been suggested as a model to explain wide angle tail radio
sources (WAT's). Based on this model, we simulate the longslit spectra of these
regions and compare the results with the observations.
