The Dynamics of Radio Galaxies In Clusters: Morphological Interactions and Particle Evolution
2020-06
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The Dynamics of Radio Galaxies In Clusters: Morphological Interactions and Particle Evolution
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2020-06
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In this thesis, I explore the dynamics of radio galaxies in galaxy clusters by studying the statistical influence of the intracluster medium on the morphology of radio galaxies, and the evolution of the electron populations within different galaxies and radio relics in Abell 2255. In Chapter 2, I study the impact of cluster environment on the morphology of a sample of 4304 extended radio galaxies from Radio Galaxy Zoo. A total of 87% of the sample lies within a projected 15 Mpc of an optically identified cluster. Brightest cluster galaxies (BCGs) are more likely than other cluster members to be radio sources, and are also moderately bent. The surface density as a function of separation from cluster center of non-BCG radio galaxies follows a power law with index -1.10+-0.03 out to 10 r_500 (~7 Mpc), which is steeper than the corresponding distribution for optically selected galaxies. Non-BCG radio galaxies are statistically more bent the closer they are to the cluster center. Within the inner 1.5 r_500 (~1 Mpc) of a cluster, non-BCG radio galaxies are statistically more bent in high-mass clusters than in low-mass clusters. Together, I find that non-BCG sources are statistically more bent in environments that exert greater ram pressure. I use the orientation of bent radio galaxies as an indicator of galaxy orbits and find that they are preferentially in radial orbits. Away from clusters, there is a large population of bent radio galaxies, limiting their use as cluster locators; however, they are still located within statistically overdense regions. I investigate the asymmetry in the tail length of sources that have their tails aligned along the radius vector from the cluster center, and find that the length of the inward-pointing tail is weakly suppressed for sources close to the center of the cluster. In Chapter 3, I present a deep and high resolution P-band (370 MHz) VLA observation of the central radio galaxies and relics in Abell 2255. Using L-band (1.5 GHz) data analyzed in Lame'e (2017), I generate maps of spectral index, alpha_PL, calculated between the two frequencies. I detect two new extended sources of very steep spectrum (alpha_PL < -2) radio emission near the center of the cluster. I analyze the spectral curvature of the Original Tailed Radio Galaxy (TRG), the Goldfish galaxy, and the NE radio relic. The spectrum of the TRG and Goldfish both exhibit curvature intermediate between a power law spectrum and the exponential cut-off spectrum of the Jaffe-Perola model (Jaffe & Perola, 1973). There are two thin filaments at the end of the TRG; filament F1 only has a reliable measurement of the spectrum at one position, and is consistent with having the same spectral shape as the tail itself; the spectrum of filament F2 has less curvature than the tail, and is consistent with a power law. This suggests that F2 has been reaccelerated by a shock in the ICM, which would also explain its morphology, although that does not work for F1. The southern component of the NE relic has values of alpha_PL ranging between -0.4 and -1.4, consistent with previous observations across similar frequencies. Systematic problems with the in-band spectral index at 1.5 GHz make quantitative claims about the spectral curvature difficult, but the extremely steep values of alpha_LL are not consistent with a shock reaccelerated power law spectrum.
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University of Minnesota M.S. thesis.June 2020. Major: Astrophysics. Advisor: Lawrence Rudnick. 1 computer file (PDF); ix, 82 pages.
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Garon, Avery. (2020). The Dynamics of Radio Galaxies In Clusters: Morphological Interactions and Particle Evolution. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/216084.
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