Jet cocoons in rotating Seyfert galaxies: adaptive three-dimensional hydrodynamics

The narrow-line regions of some Seyfert galaxies show evidence for nuclear jets interacting with the rotating interstellar gas; this is shown by point -symmetric emission-line structures in, for example, Mrk 573 and NGC 3393. We study this situation with numerical simulations of a jet in a sidewind o f uniform density but linearly increasing velocity as one moves from the so urce. We use a new three-dimensional hydrodynamic code on a binary adaptive grid. We consider two different models, one with a cocoon expansion speed higher and one with expansion speed lower than the ISM speed. We find that the model with high cocoon expansion speed is similar to results from previ ous calculations without a sidewind, except for minor asymmetries. However, model B with the slow expansion speed and fast wind speed shows considerab le qualitative differences. The jet hits and bounces off the dense cooling envelope, which is dragged by the sidewind into the straight path of the je t. The path of the jet within the cocoon is straight as long as the extende d hot cocoon acts as a shield. Once the jet hits the cold envelope of the c ocoon it is bent directly by the ram pressure of the ambient medium and fol lows a parabola of the third degree, which we derive as an analytical appro ximation for the path. The region where the jet hits the envelope is the st art of strong radio emission. This point moves towards the source with age of the jet and its bending angle. We therefore find a possible observable c orrelation between the distance of the first strong radio knot and the over all bending of jets in Seyfert galaxies. A comparison of our results with o bservations of Mrk 573 shows that the essential structural and spectral fea tures can be reproduced by choosing an appropriate viewing angle and evolut ionary stage. Looking approximately along the original jet direction a stru cture is found which strongly resembles an ionization cone. Hence caution s hould prevail when interpreting these sorts of structure within the narrow- line region of Seyfert galaxies.