Ph. D. Thesis: Matthew L. Lister

The Influence of Special Relativistic Effects on the Observed Properties of Active Galactic Nuclei

Boston University, 1999
Supervisor: Dr. Alan P. Marscher

Abstract

I investigate the properties of samples of active galactic nuclei (AGNs) selected by radio emission from the ``cores'' of their relativistic jets. As a result of relativistic beaming effects, core-selected AGN samples preferentially contain jets directed at the observer. However, they also contain lesser-aligned jets having high intrinsic luminosities and/or small cosmological distances. Prior to this work, the relative importance of these biases was unknown, and little could be inferred about the unseen ``parent'' population. My simulations show that the Caltech-Jodrell Bank flat-spectrum sample (CJF) is likely drawn from a population of ~2 x 10^7 AGNs with predominantly slow (i.e., low-Lorentz factor (Gamma)) jets.  The trend of apparent jet speed with beamed radio power in the CJF arises from observational bias, and is not indicative of a correlation L \propto Gamma^xi, where L is the intrinsic luminosity.  I find negative values of xi provide poor fits to the CJF data. I obtain good fits for xi \lesssim 0.7, but too few radio galaxies are predicted, according to the unified model.  I show that flux variability and jet bending have little effect on core-selected samples, although samples of bent jets will contain some additional high-viewing angle sources that bend toward us.

I also examine the gamma-ray emission and magnetic fields of highly beamed compact (blazar) jets. Given a tight linear correlation between gamma-ray and radio luminosity, I show that two competing gamma-ray emission models make only slightly different predictions for the observed properties of gamma-ray-selected samples. These models both predict that known gamma-ray-bright jets have higher speeds, smaller viewing angles (\lesssim 5 deg), and intrinsically fainter radio luminosities than most blazars. I find that the inner jet magnetic fields of seven blazars observed at 43 GHz are not correlated with the optical emission line strength of the host galaxy. This is in contrast to previous studies which have probed regions farther down the jet. Nearly all of the cores have magnetic fields perpendicular to the inner jet, which may be due to unresolved standing shocks.  I show that, owing to relativistic effects, the polarization properties of inner jet components are inconsistent with a population of oblique shock waves having arbitrary inclinations.

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