Theses and Dissertations - Department of Physics & Astronomy
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Browsing Theses and Dissertations - Department of Physics & Astronomy by Subject "Astronomy"
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Item Coupling semi-analytic models and N-body simulations: a new way of making galaxies and stellar halos(University of Alabama Libraries, 2017) McCord, Krista; Bailin, Jeremy; University of Alabama TuscaloosaStellar halos give insight into the initial conditions that existed when a host galaxy first formed and provide details on disrupted satellites via their different stellar populations. An algorithm that is computationally inexpensive compared to hydrodynamic simulations is necessary in order to theoretically study the structure and formation of galactic stellar halos in sufficient detail to probe substructure. CoSANG (Coupling Semi-Analytic/N-body Galaxies) is a new computational method that we are developing which couples pure dark matter N-body simulations with a semi-analytic galaxy formation model. At each timestep, results from the N-body simulation feed into the semi-analytic code, whose results feed back into the N-body code making the evolution of the dark matter and baryonic matter dependent on one another. CoSANG will enable a variety of galaxy formation science, including analysis of stellar populations, halo merging, satellite accretion, supermassive black holes, and indirect and direct dark matter detection. In this dissertation, I will describe the new simulation code CoSANG. The results from the extensive testing phase on CoSANG will be presented which indicate CoSANG is properly simulating feedback from galaxies within a dark matter halo. I used this validated code to analyze a CoSANG zoom simulation of a $10^{12} \mathrm{M_{\odot}}$ dark matter halo. Results showed a flatter inner halo near the disk and a more spherical outer halo which is expected when a galaxy exists at the center of a dark matter halo. A comparison is made with a simulation run with the same initial conditions, but with the baryonic component simulated using a hydrodynamic algorithm. The semi-analytic model predicted galaxy types better than the hydrodynamic simulation leading to the conclusion that the CoSANG halo is more accurate. I also present a dark matter direct detection analysis on the CoSANG zoom halo to measure the dark matter velocity distributions and modulation amplitudes. The CoSANG results show that the dark matter velocity distribution does not fit well to a Maxwell Boltzmann distribution and the modulation amplitudes derived indicate an anisotropic dark matter velocity distribution. Future work will include tagging dark matter particles with stellar properties to build and evolve a stellar halo.Item Diffuse ionized regions in the vicinity of active galaxies(University of Alabama Libraries, 2011) Darnell, Erin Kay; Keel, W. C.; University of Alabama TuscaloosaUsing a sample of 39 Active Galactic Nuclei (AGN), we investigated the incidence of giant ionized clouds in the vicinity of active galaxies. We carried out remote observations of the sample using the Southeastern Association for Research in Astronomy (SARA) North telescope at Kitt Peak and the SARA South telescope on Cerro Tololo. Frames were taken in continuum V and using a narrowband filter that transmits the redshifted [O III] 5007 Å line. We formed an emission line image by subtracting the combined and scaled V frames from the combined [O III] frames. To reduce uncorrelated noise, the emission line images are median filtered with a 1".9 x 1".9 box size. To bring out large diffuse regions, we convolve the emission line image with a circular Gaussian function of 3".42 FWHM. Emergent structures are determined to be starlight or ionized gas. 21 members of our sample were recently shown to be tidally disrupted in an atomic Hydrogen (HI) study. No extended [O III]-line emission clouds were seen in the vicinity of any from this group. We found one new instance of extended ionized emission clouds near the Seyfert 1 galaxy RX J1103.2-0654.Item Dust mapping of spiral galaxy disks from the Hubble starsmog survey(University of Alabama Libraries, 2016) Bradford, Sarah; Keel, W. C.; University of Alabama TuscaloosaDust in spiral galaxy disks plays an important role in observations through its interaction with starlight. While arguments have been made in favor of completely opaque spiral disks as a result of the dust (see Valentijn, 1990), most subsequent studies agree that spiral galaxies include both optically thick and optically thin regions. Using the occulting-galaxies technique introduced by White & Keel (1992), we created transmission maps of nine partially overlapped galaxy systems taken from the STARSMOG (STarlight Absorption Reduction through a Survey of Multiple Occulting Galaxies) catalog to probe the optical depth in regions of backlit dust. The measurements of all nine targets show a wide range of opacities, and therefore none of them can be definitively classified as either "optically thick" or "optically thin". In the analysis of the transmission maps of predominantly highly inclined systems, we noticed a distinct edge to the dust structure beyond which no dust was present in the foreground galaxy disk. This radius varied amongst systems but was distinct enough to be measured for three of the systems. The transmission maps also reveal a web-like pattern to the dust structure in some galaxy disks. Four of the targets showed dust structure which not only followed the pitch angle of the spiral arms, but also crossed at other various angles. This web-like pattern was only observed in systems where the foreground galaxy was of Hubble type SBc/Sc/Sbc. While there appears to be no real trend in the statistics of transmission through backlit dust with respect to stellar mass of the galaxies, there does appear to be a correlation with respect to star formation rates. In this nine-system sample, the targets with the least star formation appear more opaque. By continuing this study for the rest of the STARSMOG targets, we will be able to determine how representative this sample is of the entire target set.Item Finding fossil galaxy system progenitors using strong gravitational lensing(University of Alabama Libraries, 2018) Johnson, Lucas Edward; Irwin, Jimmy A.; University of Alabama TuscaloosaFossil galaxy systems have been described as some of the oldest systems in the universe, where the central galaxy has cannibalized most nearby member galaxies over cosmic time. While the progenitors to fossil systems have been predicted to exist in numerical simulations, little effort has gone into locating them until now. The discovery of fossil progenitors in the CASSOWARY catalog of strong gravitational lensing demonstrates that not all fossils are old, and their formation histories are more complex than originally thought. These progenitors have optical characteristics consistent with them being the transition phase between non-fossils and fossils, as we are observing the central galaxies in mid-assembly. We also identify a bias where systems acting as strong gravitational lenses are ~5 times more likely to be seen as fossils than non-lensing systems. Chandra X-ray images of eight CASSOWARY fossil progenitors show them being significantly over-luminous and hotter than comparable non-fossils which could be due to the strong lensing bias in our data, or fossils have characteristically deeper potential wells than non-fossils. Two progenitors were luminous enough to see a rise in gas temperature toward their cores which suggests these may be undergoing group mergers akin to the previously studied progenitor CSWA 2 verifying this as a viable fossil formation mechanism. Refinements to our original CASSOWARY data using the Hubble Space Telescope allowed us to disentangle complex merging environments at the centers of these eight progenitors, which further solidified the notion that progenitors are indeed transitioning toward fossil systems.Item Investigating the effects of progenitor metallicity on observable features of chandrasekhar mass type ia supernovae and improving detonation models of sub-chandrasekhar mass type ia supernovae(University of Alabama Libraries, 2018) Miles, Broxton Jake; Townsley, Dean M.; University of Alabama TuscaloosaType Ia Supernovae are generally considered to be the result of the thermonuclear disruption of carbon oxygen white dwarfs. However, the exact mechanism behind the explosion remains uncertain. The pre-explosion progenitor of a white dwarf has never been observed, so all conclusions must be drawn from comparisons between observed events and computational models. Here, work is presented on identifying spectral features indicative of progenitor metallicity. Metallicity affects the production of alpha-chain elements, which leaves imprints in the spectra. Two features are found that may be signals of progenitor metallicity, a Ti feature at 4200 \AA\ and an Fe feature at 5500 \AA . The second portion of this work focuses on the accurate modeling of detonations in sub-Chandrasekhar mass type Ia supernovae. The scales of the burning processes involved, compared to the size of the white dwarf, make fully resolving the detonation computationally impossible in full-star simulations. To mitigate this problem, past studies have used sub-grid scale models that attempt to capture the energetics of the explosion and post-process the results to calculate their models' nucleosynthetic products. If sub-grid models are to be believed, they must have accurate treatments of detonation physics such as curvature and shock strengthening. In low-density regions of the white dwarf, the curvature of the detonation front slows its propagation, affecting the production of intermediate mass elements. We find that the sharp density gradient in the outer radii of the white dwarf counteracts the weakening effect of curvature, resulting in more complete burning than expected in this low density region.Item Measuring ultraviolet extinction with GALEX in overlapping galaxies(University of Alabama Libraries, 2011) Manning, Anna; Keel, W. C.; University of Alabama TuscaloosaDust in spiral galaxies is an all encompassing factor in star formation history, measurements of luminosity, and galaxy dynamics. To learn more about galaxy formation and the influence of dust, White & Keel 1992 formulated a direct method to estimate optical depth. In the past few years, with the aid of the Galaxy Zoo forum and its members, known as zooites, a scientifically acceptable number of galaxy pairs have been identified to create a full catalog for this particular research. The White & Keel 1992 method uses differential photometry which eliminates many of the errors that plague statistical techniques that rely on the internal structure of a galaxy to estimate optical depth. The method relies heavily on the symmetry of the galaxies that make up the pair. To fulfill the symmetry requirement of the ideal geometry, the most suitable pair consists of a foreground spiral backlit by an elliptical galaxy. As evidenced here, non-interacting visually symmetric galaxies pairs yield the best results. Observations at the WIYN telescope combined with exposures downloaded from the GALEX archive are used to estimate the optical depth in these pairs as outlined by White & Keel 1992 and additionally, to trace the star formation in UV detections. Two examples of extended dust far beyond the optical radius were observed and analyzed for extinction. In this sample of galaxies, the optical depth of each wavelength scaled to the B filter was generally constant across the wavelengths observed. The effects of clumpy dust structure in the spiral arms dominated the reddening law which likely resulted in an overestimate of the optical depth measurements.Item Quantitative analysis of 3-arm spiral galaxies(University of Alabama Libraries, 2019) Hancock, Colin; Keel, William C.; University of Alabama TuscaloosaA relatively small fraction of spiral galaxies has three spiral arms. It has been theorized that these "3-arm spirals" are relatively unstable and prone to decaying into even numbered patterns due to tidal interactions. We present a series of quantitative analyses on a large sample of 3-arm spiral galaxies selected by the Galaxy Zoo 2 group. Much of this analysis used the image processing interface known as the Spiral Arc Finder and Reporter (SpArcFiRe). This program traced spiral arms on submitted images of galaxies and provided information that allowed us to replicate the arms in another program like MS Excel. Most of our work involved images taken from the Sloan Digital Sky Survey (SDSS), supplemented with high-resolution Hubble Space Telescope (HST) observations. This allowed us to study the morphological demographics of our sample, for both the internal structure and arm symmetry. The HST images provided special insight into spiral structure and star formation for these galaxies. We analyzed the star formation in particular using the MIRA AL software for photometry. We also attempted in improve the signal-to-noise of our images using data from the Stripe 82 region of SDSS. Unexpectedly, 3-arm patterns coexist with strong central bars roughly as often as other spiral patterns. We also found that 3-arm spirals do not preferentially exist in low-density regions and may be triggered by interactions.Item Simulating dwarf-dwarf galaxy flyby interactions(University of Alabama Libraries, 2018) Timsina, Ashok; Bailin, Jeremy; University of Alabama TuscaloosaThis thesis presents the N-body simulation results for the interaction between two equal mass dwarf galaxies. We studied how flyby interactions can cause a different level of disturbance on the dwarf galaxies with the help of four different simulations and measured the departure from their equilibrium state during the interactions. We performed the simulations using N-body code ChaNGa. Initially, we make sure that the interacting galaxies are in an equilibrium state separated by 100 kpc. We established the motion of one galaxy towards another galaxy, which is at rest. We designed the interactions to be increasingly strong by setting the components of velocity and finally we studied the distortion on the galaxies by using Fourier analysis looking at modes m = 1 and m = 2. This analysis allowed us to determine the minimum tidal force required for galaxy distortion.Item X-ray observations of hot gas in early-type galaxies and groups of galaxies(University of Alabama Libraries, 2013) Su, Yuanyuan; White, Raymond E.; Irwin, Jimmy A.; University of Alabama TuscaloosaMost of the baryonic matter in the Universe is not locked in stars. Instead, groups and clusters of galaxies as well as early-type galaxies contain a large mass of baryons in X-ray emitting hot gas. The study of such hot gas provides us a better understanding not only about the evolution of hierarchical structure formation and metal enrichment processes but also about baryon physics such as radiative cooling, ram pressure stripping, heating from active galactic nucleus (AGNs) and galactic winds. Moreover, such knowledge is invaluable for us to probe cosmology through galaxy clusters. In this dissertation I investigated the hot gas properties of galaxies and galaxy groups in three major scientific projects: (1) The measured metal abundance of the hot gas in early-type galaxies has been known to be lower than theoretical expectations. This may be related to the dilution of hot gas by mixing with cold gas. We studied the hot gas metal abundance with a sample of 32 early-type galaxies observed by Chandra and XMM-Newton. We find that there is virtually no correlation between hot gas Fe abundances and their atomic gas content. In contrast, we demonstrate a negative correlation between the measured hot gas Fe abundance and the ratio of molecular gas mass to hot gas mass. (2) We studied the X-ray brightest fossil group (poor cluster) ESO~3060170 out to its virial radius with Suzaku. The entropy and pressure profiles in the outer regions are flatter than in simulated clusters, similar to what is seen in observations of massive clusters. This may indicate that the gas is clumpy and/or the gas has been redistributed. (3) The nearby group centered on its bright central galaxy NGC~1407 has been thought to be an unusually dark system from previous kinematic studies. It is also known for hosting a bright galaxy NGC~1400 with a huge radial velocity difference (1200 km s$^{-1}$) with respect to the group center. We investigated the NGC~1407/1400 complex with XMM-Newton and Chandra observations. We show that a region of enhanced surface brightness between NGC~1407 and NGC~1400 is likely to be hot gas stripped from NGC~1400's ISM. We inferred that NGC~1407 system has a normal mass-to-light ratio from an X-ray--determined hydrostatic mass estimate.