Second-epoch, high-resolution observations of a low-redshift quasar sample
Date
1993
Authors
Lister, Matthew Leigh
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Abstract
Second-epoch VLA observations made at 2 and 6 cm are presented for a sample of 38 low-redshift radio loud quasars. The sample, first observed by Gower and Hutchings (1984), contains a variety of source morphologies, including classical double-lobed, one-sided, and compact structures, and has extensive optical data published by John Hutchings.
Variability of the central core component at 6 cm is examined and found to be present in 9 out of 23 double-sided sources, 0 out of 6 one-sided sources, and 3 out of 4 core-dominated sources. No apparent differences in the spectral index distributions of the variable and non-variable cores were found. This is most likely due to the inclusion of weak (< 10²⁴·⁵ W Hz⁻¹ at 6 cm), variable cores in the sample, all of which had steep spectral indices.
It is currently unclear to what extent the observed properties of radio quasars are affected by orientation and relativistic beaming effects, with some authors proposing that quasars are objects lying close to the line of sight (eg. Barthel 1989). Numerical modelling experiments are carried out which show that many of the morphological properties of this class can be explained by a randomly-oriented quasar sample containing a bias which excludes objects lying near the plane of the sky.
The ratio of core to extended luminosity, generally considered to be a strong indicator of beaming, is shown not to correlate with the orientation of the lobe structure, but rather is found to be consistent with the evolutionary scheme of Hutchings, Price and Gower (1988). No correlations between this luminosity ratio and core variability were found.
Correlations were found between the radio core luminosity and host galaxy/nuclear magnitudes, with a weaker correlation found between radio core luminosity and host galaxy colour. The ratio of the optical luminosity of the nucleus to that of the host galaxy was not found to correlate with the other radio properties of the sample.
Finally, the high-resolution maps made at 1.3 and 2 cm reveal examples of small-scale structure in several sources that would be good candidates for VLBI study.
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UN SDG 14: Life Below Water