Annu. Rev. Astron. Astrophys. 1997. 35: 607-36 Copyright © 1997 by Annual Reviews. All rights reserved

5. CONCLUSION

Extensive VLBI monitoring studies at centimeter and millimeter wavelengths, enhanced by spectral and polarization imaging, of representative types of AGN can discriminate detailed physical models. When combined with broadband total flux density and polarization observations, and especially with X-ray and -ray data that measure the synchrotron self-Compton radiation component, they can be used to determine the overall physical conditions in parsec-scale radio jets. Here is an excellent opportunity to directly compare theoretical predictions with observational data, despite the complexity and the large number of free parameters of theoretical models. Some of the most intriguing areas where this may soon become feasible include the formation of the jets, possible jet acceleration mechanisms, the nature of any nonrelativistic matter involved (e.g. the ambient medium and thermal outflows), and the influence of the central region on the jet dynamics.

Acknowledgment

I thank Thomas Krichbaum for extensive discussions and helpful suggestions on the subject of this review. Thanks are also owed to K Kellermann, A Patnaik, and A Witzel for critical comments on the manuscript. I am grateful to B Cotton, V Dhawan, K Kellermann, T Krichbaum, G Taylor, and R Vermeulen for permission to reproduce material, partly in advance of publication.