AbstractIn this thesis, I use radio observations to examine large scale jet bends in nearby radio galaxies. I complement the radio data with optical and X-ray observations in order to create a detailed picture of the host environment of these sources and explain the unusual jet structures.
I present a detailed radio study of the low-power FR I-type radio galaxy NGC 7385, using archived and new VLA observations. I find evidence for a 180 degree jet bend, and interpret this to be due to a jet-cloud interaction causing disruption of the path of the jet. This cloud is visible in HST images of the galaxy, and I discuss the possible origins and excitation mechanisms for this cloud. I examine the rotation measure structure in the interacting region, and suggest that the estimated magnetic field is due to entrainment of the cloud into the boundary layers of the radio jet. I also report the discovery of optical and X-ray emission from the brighter radio jet using data from HST and Chandra. The jet has a projected length of 5 kpc and a similar morphology to other known optical jets in low-power radio galaxies. The spectral energy distribution from radio to X-ray shows the synchrotron process to be responsible for the emission at all wavelengths.
The radio galaxy NGC 6109 is a second source exhibiting a large scale jet bend in the form of a remarkable swirl-like structure. I present an in-depth analysis of the radio emission associated with this galaxy and I discuss the possible mechanisms which could lead to such a morphology. I use polarisation studies to investigate the magnetic field structure and carry out rotation measure synthesis to explore possible interactions between the jet and the external environment. I find no evidence for optical features associated with the radio emission or any X-ray structure beyond the core. I suggest that an interaction with magnetised plasma could produce the observed jet bend, although jet precession on a kpc scale is also viable. Low frequency radio observations (e.g. LOFAR) are required to constrain these mechanisms further.
Observations of such extreme jet distortions are rare and offer the chance to examine how emission from radio galaxies can be influenced by the external environment and in turn how local IGM material is disrupted by collisions with radio jets. I discuss a few jet distortions observed in quasars and CSS sources and present observations of NGC 7016, which shows a similar jet bend to NGC 6109. I draw parallels between the two sources, and suggest that such swirl-like features could be produced as a result of interactions with trails of radio plasma. Finally, I discuss the prevalence of large scale jet bends within radio galaxy samples and give details of future surveys and instruments which should constrain the jet dynamics within NGC 7385 and NGC 6109 and have the potential to reveal a large number of similar sources in the radio sky.
|Date of Award||20 Jun 2017|
|Supervisor||Mark Birkinshaw (Supervisor) & Diana M Worrall (Supervisor)|