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Session 112 - Radio Galaxies and Jets: VLBI.
Oral session, Thursday, January 18
1st Floor, La Villita Assembly Building
A detail study of physics and evolution of the parsec--scale jet in 3C\,345 has been conveyed. The study is based on multi--frequency VLBI monitoring of the source from 1979 through 1994. 13 new VLBI observations at 5, 8, 11, and 22\,GHz have been made, covering the epochs starting from 1989.25. Main topics of the study include morphologic, kinematic, flux and synchrotron spectrum evolution of the jet.
Trajectories, proper motions, and kinematics of the jet enhanced emission regions (bright components) are measured and discussed in various model frameworks. We show that intrinsic acceleration of the bright components is required to explain their observed kinematic and luminosity evolutions. The observed global evolution of the jet reveals higher acceleration of the younger jet components, suggesting possible long--term changes of the jet direction.
For studying spectral properties of the jet, a method of broad band synchrotron spectrum fitting has been developed. The method allows to calculate the turnover frequency, turnover flux and integrated flux, using either gaussian model fits (discrete spectral fitting) and VLBI images (continuous spectral fitting). The discrete spectral fitting is used for reconstructing the component spectral and luminosity evolutions. The continuous spectral fitting is applied to VLBI images, to produce turnover frequency distribution maps, and detect fine spectral changes along and across the jet.
The results from kinematic and spectral parts of the study were combined with the observed flux evolution and morphologic changes, in order to verify the applicability of shock models, and investigate physical conditions in the jet. We show that brightest jet features are consistent with relativistic shocks, and that shocks are most prominent in the immediate vicinity of the nucleus (\approx 5\,pc projected distance). A transition from shock--dominated to plasma interaction--dominated emission regime is likely to take place in the jet at larger scales.
