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Session 16 - Low Luminosity AGN.
Oral session, Monday, June 10
Union Theater,
This thesis focuses on understanding the physical mechanisms, the structures and the dynamics of extragalactic radio sources. Our methods center upon extracting the information contained in the observed synchrotron spectrum. This work includes both original radio observations as well as an analysis of existing data.
Through a re-examination of the data taken by Carilli et al. (1991) of Cygnus A, we find, contrary to previous analysis, that a single curved spectrum can explain the spectral variations in the entire radio source. We then use the shape of the curved spectrum to disentangle the synchrotron parameters; we identify rings and a channel in the eastern lobe of Cygnus A which are most likely density enhanced features.
We observed the Fanaroff and Riley (1974) type I (FR I) source 3C449 at three frequencies with the VLA in an effort to determine the shape of the synchrotron spectrum just after the particles are initially accelerated. We find that the injection spectrum is a power law and that there is little variation in the spectrum of the jet for 50 kpc. However, our results show that the jet is embedded in a steeper spectrum sheath.
We supplemented pre-existing data of two Wide Angle Tail (WAT) sources with new observations taken with the VLA. We find that these WATs, like 3C449, have flat spectrum jets surrounded by steep spectrum sheaths. The two component structure of 3C449 and the WATs has not only been led to mistakes in previous spectral analyses, but also impacts the general models of FR I sources which were thought to have simple structures and dynamics.
We added our VLA and VLBA observations of two Compact Steep Spectrum sources (CSSs) to pre-existing MERLIN observations. We find that both of these sources (3C67 and 3C190) have complex spectral structures. In addition, 3C190 appears to have a steep injection index which leads to a 50 kyr age, much younger than larger sources. As with all the sources studied in this thesis, however, a careful analysis recognizing the contributions and confusion due to multiple spectral components, needs to be carried out.
