Parsec-Scale Structure in the Nuclei of Double-Lobed Radio Quasars

Quasars;radio astronomy

Hough, David Hans ; Readhead, Anthony C. S.

University:California Institute of Technology

Department:Physics, Mathematics and Astronomy

关键词: Quasars;    radio astronomy;   

Others  :  https://thesis.library.caltech.edu/3434/1/Hough_dh_1986.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

A complete sample of double-lobed quasars is defined, which is believed to be randomly oriented and which contains many objects with central components accessible to very-long-baseline interferometry (VLSI). The purpose of defining the sample in this way is to facilitate tests of physical models proposed to explain both the compact and extended structures in extragalactic radio sources. Statistical studies of the properties of these objects on the >~ kiloparsec scale are consistent with the assumption of random orientations and the simple relativistic beaming theory.

The central components of six double-lobed quasars have been mapped at high resolution and high sensitivity with VLBI. Each object exhibits a double or extended structure on the the ~parsec scale. This structure can be interpreted as a "core-jet," the same morphology found in the dominant cores of powerful flat-spectrum sources, thus indicating a relation between the two classes of compact radio source. The presumed VLBI jets are all fairly well aligned with >~kiloparsec-scale, one-sided jets. The fact that the VLBI and large-scale jets always lie on the same side of the compact core suggests the same cause for the asymmetric structure on both scales.

The central components of 3C245 and 3C263 have been mapped at three epochs. We find superluminal expansion in 3C263 with an apparent velocity of ~1.5c, and argue that there is evidence that 3C245 will also be found to be superluminal. These results are consistent with the simple beaming theory. It is thus clear that we will be able to measure component motion in many of these objects, which will permit us to distinguish among alternative theories of parsec-scale structure and motion.

The future study of these compact central components will benefit greatly from the increased resolution afforded by both higher frequency, ground-based VLBI and VLBI using a radio telescope in Earth orbit.