Browsing by Subject "galaxy clusters"

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    The Dynamics of Radio Galaxies In Clusters: Morphological Interactions and Particle Evolution
    (2020-06) Garon, Avery
    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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    Free-form Lens Reconstruction of Hubble Frontier Fields Galaxy Clusters
    (2018-09) Sebesta, Kevin
    Galaxy clusters, because of their massive size, act as powerful lenses for background objects. The Hubble Frontier Fields project was a multiyear international colloboration to examine six galaxy clusters acting as gravitational lenses with the aide of the Hubble Space Telescope. Lens modelling teams used shared data to reconstruct the cluster mass distributions using a variety of methods. We used our free-form method Grale to solve for the mass distribution of each cluster. The only inputs used were related to the observed images, and unlike most other methods, no information about visible light of the cluster galaxies was part of the input. The lensing models produced by each modelling team were used to study magnified high redshift galaxies, and construct their luminosity functions. These scientific advances prepare the community ahead of the James Webb Space Telescope launch. Upon reconstructing the cluster distributions, our goal was to see if light traces mass and investigate Grale uncertainties. We focused on the first two Hubble Frontier Fields clusters, Abell 2744 and MACS J0416. No significant offsets were found between brightest cluster member galaxies and local mass peaks for either cluster on scales of ≈ 10 − 15kpc. We calculated the correlation function between cluster core member galaxies and mass distribution for each cluster. Our results confirmed the standard biasing scenario of galaxy formation, meaning the clustering of galaxies is heavily influenced by the underlying dark matter distribution. We found light traces mass within HFF clusters, Abell 2744 and MACS J0416. We directly compared two Abell 2744 Grale reconstructions to gauge the robustness of calculated uncertainties, and confirmed that Grale uncertainties were robust to changes in input data and slight modifications in the Grale code parameters. Moreover, both maps produced relatively low Lens-plane RMS values, comparable to those of other methods. We explained our method for calculating Lens-plane RMS, while also providing multiple alter- native definitions, because of a lack of consensus on the subject in the published literature.