This thesis presents my recent investigations of the tenuous intracluster medium (ICM) in galaxy clusters using radio observations.The ICM is composed primarily of thermal and nonthermal plasma populations, permeated by magnetic fields which influence their evolution. Radio observations provide unique probes of the properties of the ICM, allowing for estimation of particle densities, magnetic field strengths, and even yielding clues to the physical mechanisms of particle acceleration.A major theme of this dissertation is that faint diffuse radio emission may contribute a significant amount of the synchrotron luminosity in galaxy clusters, yet goes unobserved due to an underappreciated deficiency of interferometric radio telescopes. Some of the current physical models do not account for this low surface brightness synchrotron emission, which may hold the key to distinguishing between competing models of relativistic particle acceleration and magnetic field amplification in these low density environments.I first discuss the use of polarization observations to probe magnetized plasmas, exploring various methods of Faraday rotation measure determination.I demonstrate that methods such as traditional fitting of models to polarization angle only (without consideration of the fractional polarization) or the novel Rotation Measure Synthesis may yield erroneous results in the presence of complex Faraday structure. The best way to more accurately recover the true Faraday structure is by fitting models directly to the observables Q and U, using radio polarization observations of the southern lobe of the radio galaxy 3C33 as an example.Next I exhibit results from a 1.4~GHz GBT study of twelve merging galaxy clusters.After subtraction of confusion from Galactic foreground and extragalactic background radio sources, eleven of the twelve clusters exhibited a significant excess of diffuse emission over that found by previous interferometric studies. Faint large-scale radio emission in clusters may be commonly missed by interferometric studies, particularly at low redshifts, and this has serious implications for models of halo generation.I also provide supporting evidence for the notion that the total radio emission in clusters may not depend strongly on the particular structure (e.g., halo, relic).The energy for particle acceleration is channeled from the merger and tied observationally to the thermal state of the ICM, and can result in a variety of radio structures.I then present the results of snapshot VLA observations of the minor merging cluster A2142 at 1.4~GHz. New evidence of large scale ICM sloshing has been discovered in this cluster, further supported by an apparent 2~Mpc radio halo discovered as part of our recent GBT study.My VLA observations confirm the presence of a Mpc-scale halo in the sloshing core of A2142, which extends beyond the central cold fronts -- a phenomenon unobserved in systems lacking major merging activity.This new halo appears to be comprised of multiple components, with a sharply peaked mini-halo type structure in the core, and a faint, extended giant radio halo type structure extending beyond the core region.The VLA observations do not recover the full halo extent observed by previous GBT observations, illustrating a weakness of interferometric cluster observations that may be underestimated in the literature.Preliminary spectral analysis finds a steep spectrum (alpha > 1.5) to the core emission, possibly indicating a turbulent origin for the cosmic ray production in that region. Finally, I discuss preliminary findings of a recent GBT study of nine clusters, chosen to span a wide range of dynamical activity. I found evidence for low surface brightness emission missed by interferometers in eight of the nine clusters, including two new radio structures.Additionally, I found more evidence that the total radio luminosity of clusters hosting diffuse emission follows the radio - X-ray correlation regardless of the structure of the radio emission (e.g., halo, relic, or combination).
University of Minnesota Ph.D. dissertation. December 2013. Major: Astrophysics. Advisor: Lawrence Rudnick. 1 computer file (PDF); xii, 198 pages.
Investigating the thermal and nonthermal properties of galaxy clusters with radio observations.
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