IRAS 04210+0400 : Modeling the optical spectra from flaring large scale jets

The emission-lines in the active galaxy IRAS 0421+0400 show a dramatic (∼ 900km s) increase in the velocity spread at the position of radio hot-spots which are located at the beginning of extended radio lobes. We study a simple geometric model of an opening outflow which reproduces the structure found in the long-slit emission-line spectrum of the hot-spot regions. The predicted bifurcations in the optical image structure of these regions is confirmed by deep [Oiii]-5007Å line-imaging. We propose that this phenomenon is the result of a jet emerging from the galaxy through the boundary between the interstellar and intergalactic medium. A similar model has previously been suggested as an explanation for wide angle tail radio sources (WAT’s). If our model proves to be correct in more detailed future observations, then IRAS 0421+0400 provides the unique possibility to study the flaring jet phenomenon at optical wavelengths.