The impact of red giant/AGB winds on AGN jet propagation

Dense stellar winds may mass-load the jets of active galactic nuclei, although it is unclear what are the time and spatial scales in which the mixing takes place. We study the first steps of the interaction between jets and stellar winds, and also the scales at which the stellar wind may mix with the jet and mass-load it. We present a detailed two-dimensional simulation, including thermal cooling, of a bubble formed by the wind of a star. We also study the first interaction of the wind bubble with the jet using a three-dimensional simulation in which the star enters the jet. Stability analysis is carried out for the shocked wind structure, to evaluate the distances over which the jet-dragged wind, which forms a tail, can propagate without mixing with the jet flow. The two-dimensional simulations point at quick wind bubble expansion and fragmentation after about one bubble shock crossing time. Three-dimensional simulations and stability analysis point at local mixing in the case of strong perturbations and relatively small density ratios between the jet and the jet dragged-wind, and to a possibly more stable shocked wind structure at the phase of maximum tail mass flux. Analytical estimates also indicate that very early stages of the star jet-penetration time may be also relevant for mass loading. The combination of these and previous results from the literature suggest highly unstable interaction structures and efficient wind-jet flow mixing on the scale of the jet interaction height, possibly producing strong inhomogeneities within the jet. In addition, the initial wind bubble shocked by the jet leads to a transient, large interaction surface. The interaction structure can be a source of significant non-thermal emission.