Gigahertz-Peaked Spectrum Radio Sources

Abstract

The study of compact active galactic nuclei (AGN) that possess convex radio spectra (the gigahertz-peaked spectrum radio sources) offers a unique opportunity to probe both the early evolutionary stages of relativistic AGN jets and their immediate nuclear environments. In this article I trace Ken Kellermann's early investigations of these sources, which played a major role in justifying the development of modern-day VLBI techniques. I describe how our understanding of these AGN has progressed since Kellermann's early discoveries, and discuss several ways in which the current classification scheme can be simplified to reflect intrinsic source characteristics, rather than observer-biased quantities. Finally, I discuss recent results from the VLBA 2 cm survey concerning the relativistic jet kinematics of the two-sided peaked-spectrum sources 4C +12.50 (PKS 1345+125) and OQ 208 (1404+286).