Physics and Kinematics of the Parsec Scale Jet of the Quasar 3C345

The quasar 3C 345 is one of the archetypical examples of an active galactic nucleus (AGN) featuring a complex parsec-scale jet with a pronounced helical morphology and a range of distinct emitting regions moving at apparent superluminal speeds. The thesis at hand presents results from a study of the long-term jet evolution, with a particular focus on the evolution of trajectories, kinematics, and emission in more than 20 distinct regions embedded in the jet over a period of over 30 years. Unique insights into the longterm evolution of the parsec-scale radio emission were gained from the formation of an unprecedented database comprising over 300 archival and new observations. The effect of frequency dependent opacity has been investigated, providing evidence for position variability of the observed origin of the jet, relating to changes in the viewing angle and to the activity state of the jet. A ”closeup” on physical properties of individual features implied that shocks dissipate at distances of about 2 mas (150 pc de-projected distance) and the outer jet is most likely dominated by Kelvin-Helmholtz instabilities. 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 high activity states. The longterm evolution of this pattern indicates its possible relation to the elliptical mode of Kelvin-Helmholtz instability. In the present work, special attention is paid to the onset of a new period of high activity in the source that began in 2008, which has been observed from radio through gamma-rays. The relation between the radio/optical emission and the production of high energy photons in 3C 345 has been investigated. This provided the first identification of gamma-ray emission from 3C 345 and the nearby quasar NRAO 512. Observations with the Very Long Baseline Array (VLBA) reveal morphology and kinematics of the flow on scales of up to approximately 5 mas (de-projected linear distances of 380 pc). Evolution of the gamma-ray, optical, and parsec-scale radio emission indicated similar physical origins based on long-term trends and on a shock-shock interaction scenario for short events. All short gamma-ray events are explained in a single framework, directly connecting moving features observed in the radio jet with high energy emission. The observations indicate that both the quiescent and flaring components of the gamma-ray emission are produced in a region of the jet of about 25 pc in extent. This region marks the Compton-loss dominated zone of the flow and its large extent may favor the synchrotron self-Compton mechanism for gamma-ray production in the relativistic jet of the quasar 3C 345