Observations and Gas Dynamics of Extragalactic Radio Jets

Citation

Lind, Kevin Robert (1987) Observations and Gas Dynamics of Extragalactic Radio Jets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wnqa-gn45. https://resolver.caltech.edu/CaltechETD:etd-09092008-091639

Abstract

This thesis is a combined observational and theoretical study of extragalactic radio jets. Jets are defined observationally as extended, center-brightened features, which are observed in radio images at all resolution scales. They are defined theoretically as momentum-dominated, well-collimated plasma flows. There is now little debate as to the basic interpretation of radio jets as actual plasma outflows, but the detailed dynamics of the jets, or even whether the kiloparsec-scale jets are relativistic, are still uncertain. The resolution of the details of the physics of jets requires improved radio images, especially at the base of the jet, and detailed models of jets. Maps of the base of the radio jet can only be obtained with VLBI observations; detailed jet models require numerical simulations on a supercomputer.

The observational work was a large global VLBI observation of the N galaxy 3C371. The goal was to detect and, if possible, map the underlying jet. This was done, and the results compared with a previous VLBI map, and with maps from other interferometers at lower resolution. No conclusions could be drawn regarding the nature of the jet, although it was clear that the jet was active, and appeared to vary on short time scales.

The theoretical work was in two parts, both of which were directed toward refining existing theories. The first part was to calculate the emission for relativistically moving patterns which themselves contain relativistic flows, to determine how much the flux as a function of viewing angle may vary between realistic models of the knots in relativistic jets. It was found that considerable variation was possible, and that superluminal expansion rates were not necessarily good determiners of the bulk flow rate. The second part was to develop a code to simulate axisymmetric magnetized jets propagating into a uniform medium. This was implemented for the case of toroidal field only, and run for a moderately magnetized injected jet. It was found that, although most of the jet dynamics was determined by the nonmagnetic forces, the influence of the magnetic tension focused the flow sufficiently to significantly increase the speed of advance of the jet.

Thesis Files