The long-term evolution of the parsec scale jet of the quasar 3C 345

The quasar 3C 345 is one of the best examples of an active galactic nucleus (AGN) showing structural and flux variability on parsec scales around a compact unresolved radio core. Over the past 30 years, it has been followed up closely from radio to gamma-ray wavebands with a special focus on very long baseline interferometry (VLBI) observations in the range of 1-100 GHz. The complex parsec-scale jet of 3C 345 exemplifies an archetypical 'superluminal' jet with an apparent helical morphology. Here we present first results from a study of the long-term jet evolution, especially focusing on the evolution of trajectories, kinematics, and emission in more than 20 enhanced emission regions embedded in the jet. A "closeup" on physical properties of individual features implies that the outer jet is most likely dominated by Kelvin-Helmholtz instability. Studies of general trends in properties of those features provide certain evidence for their apparent trajectories to result from an underlying (slowly evolving) pattern lit up by passages of plasma condensations ejected during the nuclear flares. The long-term evolution of this pattern indicates its possible relation either to the elliptical mode of Kelvin-Helmholtz instability or precession of the jet direction.