Astronomy Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2746
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Item PHYSICAL CONDITIONS OF THE MULTI-PHASE INTERSTELLAR MEDIUM IN NEARBY GALAXIES FROM INFRARED AND MILLIMETER-WAVE SPECTROSCOPY(2022) Tarantino, Elizabeth; Bolatto, Alberto D; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Gas and dust in the interstellar medium (ISM) cools and condenses, gravitationally collapses, and forms stars. At the same time, stars can heat and ionize their surroundings, influencing the physical conditions of the nearby ISM. In this thesis, I take a multi-wavelength, spectroscopic approach to investigate the physical conditions of the multi-phase ISM in nearby galaxies. The [CII] fine-structure transition at 158 micron is frequently the brightest far-infrared line in galaxies and can trace the ionized, atomic, and molecular phases of the ISM. I present velocity-resolved [CII] observations from SOFIA in the nearby galaxies M101 and NGC 6946 and determine that [CII] emission is associated with the atomic and molecular gas about equally, with little contribution from the ionized gas. Using the [CII] cooling function, I calculate the thermal pressure of the cold neutral medium and find that the high star formation rates in our sample can drive large thermal pressures, consistent with predictions from analytical theory. Next, I investigate the properties of the ionized gas around one of the hottest and most luminous Wolf-Rayet (WR) stars in the Small Magellanic Cloud. I use spatially resolved mid-infrared Spitzer and far-infrared Herschel spectroscopy to establish the physical conditions of the ionized gas. Using the photoionization code Cloudy, I construct models with a range of constant densities between n_H = 4 - 12 cm^-3 and a stellar wind-blown cavity of 15 pc that reproduce the intensity and spatial distribution of most ionized gas emission lines. The higher ionization lines cannot be produced by the models --- however, I show that wind-driven shocks or a harder ionizing WR spectrum can explain their intensities. Lastly, I explore the properties of molecular clouds in a large (170x350 pc) map of an active star-forming region in the Large Magellanic Cloud. Using 12CO(2-1) and 13CO(2-1) observations from the ALMA ACA, I decompose the emission into individual cloud structures and determine their sizes, linewidths, mass surface densities, and virial parameters. Almost all of the clouds are gravitationally bound or marginally bound and share similar properties to molecular clouds in the Milky Way. I do not find evidence that the surrounding star formation significantly influences the kinematic properties of the clouds through stellar feedback.Item WATER IN THE EARLY SOLAR SYSTEM: INFRARED STUDIES OF AQUEOUSLY ALTERED AND MINIMALLY PROCESSED ASTEROIDS(2017) McAdam, Margaret; Sunshine, Jessica M; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis investigates connections between low albedo asteroids and carbonaceous chondrite meteorites using spectroscopy. Meteorites and asteroids preserve information about the early solar system including accretion processes and parent body processes active on asteroids at these early times. One process of interest is aqueous alteration. This is the chemical reaction between coaccreted water and silicates producing hydrated minerals. Some carbonaceous chondrites have experienced extensive interactions with water through this process. Since these meteorites and their parent bodies formed close to the beginning of the Solar System, these asteroids and meteorites may provide clues to the distribution, abundance and timing of water in the Solar nebula at these times. Chapter 2 of this thesis investigates the relationships between extensively aqueously altered meteorites and their visible, near and mid-infrared spectral features in a coordinated spectral-mineralogical study. Aqueous alteration is a parent body process where initially accreted anhydrous minerals are converted into hydrated minerals in the presence of coaccreted water. Using samples of meteorites with known bulk properties, it is possible to directly connect changes in mineralogy caused by aqueous alteration with spectral features. Spectral features in the mid-infrared are found to change continuously with increasing amount of hydrated minerals or degree of alteration. Building on this result, the degrees of alteration of asteroids are estimated in a survey of new asteroid data obtained from SOFIA and IRTF as well as archived the Spitzer Space Telescope data. 75 observations of 73 asteroids are analyzed and presented in Chapter 4. Asteroids with hydrated minerals are found throughout the main belt indicating that significant ice must have been present in the disk at the time of carbonaceous asteroid accretion. Finally, some carbonaceous chondrite meteorites preserve amorphous iron-bearing materials that formed through disequilibrium condensation in the disk. These materials are readily destroyed in parent body processes so their presence indicates the meteorite/asteroid has undergone minimal parent body processes since the time of accretion. Presented in Chapter 3 is the spectral signature of meteorites that preserve significant amorphous iron-bearing materials and the identification of an asteroid, (93) Minerva, that also appears to preserve these materials.Item Wide Field of View Spectroscopy Using Fabry-Perot Interferometers(2016) Nikoleyczik, Jonathan Allen; Veilleux, Sylvain; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present a high resolution spectrometer consisting of dual solid Fabry-Perot Interferometers (FPIs). This work is intended to be an all inclusive documentation of the instrument including discussion of the design of this instrument, the methods used in data reduction, and the analysis of these data. Each FPI is made of a single piece of L-BBH2 glass which has a high index of refraction n~2.07 with a thickness on the order of 100 μm. Each is then coated with partially reflective mirrors to create a resonant cavity and thus achieve a spectral resolution of R~30,000. Running the FPIs in tandem reduces the overlapping orders and allows for a much wider free spectral range and higher contrast. We will also discuss the properties of the FPIs which we have measured. This includes the tuning of the FPIs which is achieved by adjusting the temperature and thus changing the FPI gap and the refractive index of the material. The spectrometer then moves spatially in order to get spectral information at every point in the field of view. We select spectral lines for further analysis and create maps of the line depths across the field. Using this technique we are able to measure the fluorescence of chlorophyll in plants and attempt to observe zodiacal light. In the chlorophyll analysis we are able to detect chlorophyll fluorescence using the line depth in a plant using the sky as a reference solar spectrum. This instrument has possible applications in either a cubesat or aerial observations to measure bulk plant activity over large areas.Item Modeling Optically Thick Molecular Emission Spectra of Comets Using Asymmetric Spherical Coupled Escape Probability(2014) Gersch, Alan Michael; A'Hearn, Michael F; Astronomy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Comets are frozen remnants from the formation of the Solar System. As such, their chemical composition is of great significance to understanding the origin of the planets and the distribution of important molecules, including water and other volatiles, throughout the Solar System. Recent observations, in particular those of the Deep Impact and EPOXI Missions, have provided better spectra of a cometary coma than were previously available. These observations include spectra with high spatial resolution very near to the nucleus. The purpose of this research is to better understand the abundances, distributions and creation mechanisms of various volatiles observed in cometary comae, in particular those of comet 9P/Tempel 1, the target of the Deep Impact Mission, and 103P/Hartley 2, the subject of the EPOXI mission. In order to do so, I have built a computer model of the spectrum of the comet's coma which includes the difficult and often ignored problem of accurately including radiative transfer to account for the potentially optically thick coma (or regions of the coma) near the nucleus. I have adapted Coupled Escape Probability, a new exact method of solving radiative transfer problems, from its original plane-parallel formulation for use in asymmetrical spherical situations. My model is designed specifically for use in modeling optically thick cometary comae, although not limited to such use. By providing for asymmetric geometry in the coma, the model is able to include the morphology of the near nucleus coma, as observed by the Deep Impact spacecraft for Tempel 1 and Hartley 2, and include this in the modeling of radiative transfer. This method enables the accurate modeling of comets' spectra even in the potentially optically thick regions nearest the nucleus, such as those seen in Deep Impact observations of 9P/Tempel 1 and EPOXI observations of 103P/Hartley 2. This model will facilitate analyzing the actual spectral data from the Deep Impact and EPOXI missions to better determine abundances of key volatile species, including CO, CO2 and H2O, as well as remote sensing data on active comets.