A MODEL FOR RADIO OPTICAL JETS

We develop a model in which mildly-relativistic jets propagate through the interstellar medium in active galaxies and collide with dense gas eous obstacles (supernova remnants, winds from giant stars or line-emi tting clouds for example). Shock waves result from these interactions. Particles are accelerated at the shocks and subsequently emit synchro tron emission. This model can explain the properties of radio/optical jets similar to the one observed in M 87 (knotty structure, radiation spectra, energetics etc). We show that supernova remnants and red gian t stars give at most a minor contribution to the jets' structure. Line -emitting clouds are the most probable obstacle candidates.