Observations and simulations of parsec-scale jets in active galactic nuclei

Total intensity and polarization images of the quasar 3C 345 made at 2.8 cm from global Very Long Baseline Interferometry (VLBI) observations made at epochs 1984.95 and 1986.17 are presented. The dominant magnetic field in the VLBI jet in components farther than {dollar}sim{dollar}0.5 milliarcsecond from the core appears to be longitudinal, as had been seen in 6 cm VLBI polarization images of this source. The magnetic field in one component that had recently emerged is transverse in our earlier epoch, but had becomes longitudinal by our later epoch. This is consistent with a picture in which shocks forming in the VLBI jet dominant the magnetic field structure close to the core, but not further out, where a substantial underlying longitudinal magnetic field has formed, possibly due to shear.; A series of simulated maps showing the appearance in total intensity of flows computed using a relativistic hydrodynamic code (Duncan & Hughes 1994: ApJ, 436, L119) are presented. The radiation transfer calculations were performed by assuming the flow is permeated by a magnetic field and fast particle distribution in energy equipartition, with energy density proportional to the hydrodynamic energy density (i.e., pressure) and do not include light travel time effects. We find that relativistic flows subject to strong perturbations exhibit a density structure consisting of a series of nested bow shocks, and that this structure is evident in the intensity maps for large viewing angles. However, for viewing angles {dollar}<{dollar}30{dollar}spcirc{dollar}, differential Doppler boosting leads to a knots of emission, similar to to those seen in many VLBI maps of parsec-scale jets. The integrated light curve shows features characteristic of a radio loud Active Galactic Nuclei: small amplitude variations and a large outburst.; Preliminary maps that include light travel time effects are also presented. The integrated flux light curves at different viewing angles show that the time delays smear the low level fluctuations. Relativistic effects of time dilation and Doppler boosting are demonstrated in the integrated flux light curves by increase of the frequency and amplitude of variations with decreasing viewing angle.