THE SUBPARSEC-SCALE STRUCTURE AND EVOLUTION OF CENTAURUS-A - THE NEAREST ACTIVE RADIO GALAXY

We present high-resolution VLBI radio images of the closest classical radio galaxy? Centaurus A, including the highest resolution image yet for this source. The images were made from data obtained over a period of approximately 8 yr at the frequencies of 2.3, 3.8, and 8.4 GHz wit h the Southern Hemisphere VLBI Experiment (SHEVE) array and at 2.3, 8. 4, and 22.2 GHz with the Very Long Baseline Array. We give complete de tails of the data reduction and analysis procedures. The subparsec-sca le structure of Cen A is complex, consisting of a bright jet and a fai nter counterjet. The bright jet contains components that have sublumin al speeds of approximately 0.1c and undergo irregular episodes of rapi d internal evolution. The rapid evolution sometimes observed could be interpreted as evidence for an underlying jet flow much faster (> 0.45 c) than observed from the proper motion of components (similar to 0.1c ). Considering the large-scale morphology of the sourer, the motions a nd temporal variations in the jet, and the detection of a counterjet, we conclude that the axis of the Cen A jet lies between similar to 50 degrees and similar to 80 degrees to our line of sight. We find that t he estimated times of component ejection from the compact core are rea sonably coincident with enhancements in hard X-ray intensity and 22 GH z flux density. In the context of the radio galaxy population, Cen A i s a low-luminosity FR I-type source and in general has the properties observed in other FR I radio galaxies. Overall, the observations of Ce n A presented here, and from other investigations, are consistent with the idea that sources with an FR I appearance are not aligned with ou r line of sight and have relativistic flow on the subparsec scale. The apparently subluminal subparsec-scale jet components are interpreted as being slow patterns on the relativistic flow.