Doctor of Philosophy, The Ohio State University, 2024, Physics

Stellar clusters form inside large clouds of gas, which collapse under gravity until the feedback from the newly formed stars begins to push the gas away, disrupting further star formation. In this dissertation we explore several of the feedback mechanisms responsible for stopping star formation. We will look in depth at two mechanisms in particular: Radiation pressure and cosmic ray diffusion. To analyze these pressures, we build simple models which we then expand. Radiation pressure's role depends greatly on the composition of the dust embedded in the gas the stars form from. The dust interacts with the photons from the star cluster, scattering and absorbing them, before re-radiating the photons in the infra-red. To build a more realistic model of radiation pressure, we use time dependent spectral data from simulations and realistic dust grain distributions and optical properties. The effects of cosmic ray diffusion are controlled by several parameters, such as the diffusion coefficient and the size scale of the shell of material the cosmic rays are acting on. We compare cosmic ray pressure to radiation pressure, and the pressure from hot ionized gas around the stellar cluster. We also apply our analysis of each of these pressures to observations. We do this to estimate the role of each pressure in observed regions, helping to explore the mechanisms which govern the star formation rates in star-forming regions of galaxies. Additionally, we analyze the dynamics of shells driven by radiation pressure, cosmic ray diffusion, and the pressure from hot ionized gas. From these simple dynamical models we draw conclusions about the roles of each of the pressures, and examine the parameter space where each dominates. We find that radiation pressure is highly important to the initial stages of feedback, dominating the other studied pressures for the youngest and most compact clusters. Radiation pressure can rapidly drive gas away from the central star cluster, (open full item for complete abstract)

Committee: Todd Thompson (Advisor); Andrew Heckler (Committee Member); Joanne Patterson (Committee Member); Adam Leroy (Committee Member); Christopher Hirata (Committee Member) Subjects: Astronomy; Astrophysics; Physics

Doctor of Philosophy, The Ohio State University, 2021, Astronomy

Many important elements of galaxy structure and star formation are invisible or lessened in brightness in optical images. Newly formed stars which shine incredibly bright have most of their emitted light absorbed by interstellar dust. Old, cool stars that make up interesting galaxy structures like stellar bars are outshone by bright star forming regions. In order to understand these fundamental features of galaxies infrared light is needed. Near-infrared (NIR) light can help observe light obscured or attenuated at other wavelengths. NIR light can indirectly observe light from newly born stars. When the dust grains which attenuated the high-energy light cool, that light is reprocessed into the infrared. Using a combination of high energy and infrared light a star formation rate can be calculated. In Ch. 2 I present 2′′ resolution galaxy-wide dust attenuation and star formation rate measurements for nearby, face-on galaxies NGC 5194 and NGC 6946. These measurements are calculated using two different ionizing states of Hydrogen at 6562.8 A(Hα) and 1.282 μm (Paβ). I find that attenuation drops with radius, with a bright, high attenuation inner region, and I calculate the best-fit empirical coefficients to correct for attenuation by combining Hα with 8, 12, 24, 70, or 100μm. NIR light can also help observe stellar bars, which are outshone by brighter star-forming regions in optical light. NIR light is less affected by nearby star formation. Additionally, any dust attenuation in the stellar bar would be less in the NIR than at optical wavelengths. Chapters 3 and 4 use NIR images to analyze bars. In chapter 3 I trained a convolutional neural network to identify stellar bars in galaxies. In chapter 4 I used LASSO regression, a type of an ordinary least squares regression with a penalizing term, to identify which bar and galaxy variables are the most correlated with centrally enhanced star formation. The half-light radius is the radius within half of the light of the gala (open full item for complete abstract)

Committee: Adam Leroy Ph.D. (Advisor); Paul Martini Ph.D. (Committee Member); Todd Thompson Ph.D. (Committee Member); Wuyang Hu Ph.D. (Committee Member) Subjects: Astronomy; Astrophysics

Master of Sciences, Case Western Reserve University, 2020, Geological Sciences

Glassy spherules from three Transantarctic Mountain sediments were geochemically analyzed and at two of these sites (Mt. Raymond (RY) in the Grosvenor Mountains and Meteorite Moraine (MM) in Walcott Neve, in the Beardmore Glacier region of Antarctica) Australasian microtektites were discovered. The microtektites were identified based on their pale yellow appearance and confirmed geochemically; they have high concentrations of silica (SiO2 = 60.0 +/- 6.9 wt%) and alumina (Al2O3 = 23.0 +/- 4.0 wt%) and all have K2O/Na2O > 1, characteristic of microtektites and distinct from spherules of meteoritic origin. Additionally, the trace element pattern matches the upper continental crust with enrichments in refractory elements and depletions in volatile elements, most likely as a result of melting and vaporization of the source material. The presence of Australasian microtektites in RY sediment confirms the recent Australasian strewnfield extension to Antarctica (Folco et al., 2008) and the presence of highly-depleted microtektites (Van Ginneken et al., 2018). In addition to microtektites, thousands of chondritic spherules and a few unique cosmic spherules were identified in RY, MM, and Jacobs Nunatak (JA) sediments. These sites are evidently successful cosmic dust and impact debris collectors, and thus their usefulness in recording influx events is explored.

Committee: Ralph Harvey Dr. (Committee Chair); James Van Orman Dr. (Committee Member); Steven Hauck II Dr. (Committee Member) Subjects: Geochemistry; Geology