Interactions Between Radio-Loud Active Galaxies and Their Environments

Abstract

In this dissertation, I present my work on the behaviour of different features of radio-loud active galaxies to investigate how energy is transferred from their jets to the environment. To this end, I have studied the knots in the jet in Centaurus A, the radio and X-ray emission from the lobes of the FRII radio galaxies 3C 353 and Pictor A, and the gas properties of a sample of galaxy groups some of which host radio-loud AGN. Using new and archival multi-frequency radio and X-ray data for Centaurus A obtained over almost 20 years with the Very Large Array and with Chandra, I have measured the X-ray and radio spectral indices, flux density variations, polarisation variations and proper motions of the jet knots. I used these measurements to constrain the likely knot formation mechanisms and particle acceleration processes within this jet and compared my results with the variations detected in the properties of the knots in M87. I found that none of the knots are a result of impulsive particle acceleration and that those knots that are detected in both X-ray and radio are likely due to collisions between the jet and an obstacle, while the radio only knots, the majority of which are moving, are likely due to compressions of the fluid flow. Using six frequencies of new and archival radio data and new XMM-Newton observations of 3C 353, I show that inverse-Compton emission is detected in the lobes of this source. By combining this X-ray emission with the radio synchrotron emission, I have constrained the electron population and the magnetic field energy density in the lobes of this radio galaxy. I have argued that the variations in the X-ray/radio ratio in the brighter lobe requires a changing magnetic field strength. I have extended this work using a statistical analysis of the X-ray and radio emission to show that the observed small-scale variation in surface brightness cannot be reproduced by simple combinations of the electron energy distribution and the magnetic field strength. I therefore suggest that the changes in surface brightness that give rise to the filamentary structures seen in the lobes are probably due to strong spatial variations of the magnetic field strength. Finally, I present a study of galaxy groups observed with XMM-Newton in which I measure temperature and surface brightness profiles to examine whether radio-source heating makes radioloud groups hotter and more luminous than radio-quiet groups. I compare my measurements with previous luminosity-temperature relationships and conclude that there is a significant difference in the gas properties of radio-loud and radio-quiet groups.