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Session 31 - Quasars.
Oral session, Wednesday, January 07
International Ballroom East,
We have used the VLBA at 15 GHz to image the structure of 132 strong compact AGN and quasars with a resolution better than one milliarcsec and a dynamic range typically exceeding 1000 to 1. Most of the sources we have observed show the canonical core-jet morphology. The milliarcsecond jets generally appear one- sided, but in the lower luminosity radio galaxies and in high luminosity quasars with gigahertz peaked spectra, two sided structure is not uncommon. In many cases there is significant curvature, sometimes up to 90 or even 180 degrees, particularly close to the core. In other cases the jets have a more gradual curvature. In some cases there are multiple bends or twists along the jet, suggestive of a three dimensional curved structure. Many of the jets may be described by a small number of apparently discrete components, but in other cases there appears to be a monotonically decreasing distribution of radio emission Usually the structure is unresolved along the direction perpendicular to the jet, but a few sources have jets with broad plumes.
Much of the visible parsec scale structure in compact radio sources can probably be explained as the projection of a relativistically beamed twisted jet, which appears bright at those positions where it approaches the viewer. In some low luminosity radio galaxies, the structure appears more symmetric at 2 cm than at longer wavelengths. The apparent long wavelength asymmetry in these sources is probably due to absorption by intervening ionized material.
A few sources contain only a single component with any secondary feature at least a thousand times weaker. Peak rest frame brightness temperatures are typically of the order of 10 exp(11-12) K with no evidence for any excess over the limit of 10 exp 12 K expected from inverse Compton cooling. We find no obvious correlation of radio morphology and the detection of gamma-ray emission by EGRET.
