Doctor of Philosophy, The Ohio State University, 2022, Astronomy

The composition and evolution of galaxies have been an elemental but long-standing mystery in Astronomy. In the last century, the advent of telescopes across the electromagnetic spectrum has revolutionized our perception of galaxies from a mere assembly of stars to a complex ecosystem. Both observational and theoretical studies have pointed towards the existence of a gaseous medium beyond the stellar component of galaxies, aka, the circumgalactic medium (CGM). The CGM is a multi-phase gas surrounding the stellar disk of a galaxy, filling up its dark-matter halo. The CGM is simultaneously the fuel tank, waste dump, and recycle hub of galaxies. It is expected to harbor the baryons, metals, and feedback that are missing from the stellar disk. I have studied the two extreme phases of the CGM to investigate how the feeding (accretion) and the feedback (outflow) at the galactic scale govern the evolution of the Milky Way and similar nearby galaxies. The ≥106 K hot CGM, despite being challenging to detect, is a treasure trove of galaxy evolution. By probing the hot CGM of the Milky Way (MW) using X-ray absorption lines of multiple metal ions, I have discovered a super-virial 107 K phase coexisting with the well-known virialized 106 K phase, featuring non-solar abundance ratios of light elements, α-enhancement, and non-thermal line broadening. I have also detected this super-virial phase of MW CGM in X-ray emission analyses. Detection of these surprising properties of the CGM along multiple directions in the sky suggests a strong connection between the hot CGM and past Galactic outflow(s). Observations of MW-like galaxies complement our observations of the Milky Way. I have discovered the hot CGM emission of an MW-mass galaxy NGC 3221 that is extended (~150-200 kpc) and is massive enough to account for its missing baryons. The CGM is not isothermal, with the CGM within 100 kpc of NGC 3221 being super-virial, and fainter along the minor axis than the global a (open full item for complete abstract)

Committee: Smita Mathur (Advisor); Paul Martini (Committee Member); Annika Peter (Committee Member); Adam Leroy (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, University of Toledo, 2017, Physics

A central question in the study of star formation is: what sets the mass distribution of nascent stars? This distribution appears to vary little (especially at the low mass end) throughout our galaxy and others, despite variations in the heavy element abundance, interstellar radiation field, and amount of gas available. This work is a component of the Herschel Orion Protostar Survey (HOPS), a program to characterize hundreds of protostars in the Orion Molecular Clouds, largest site of on-going star formation with 0.5 kiloparsec. As part of the HOPS program, we have spectral energy distributions with a wavelength coverage of 1.2-870 µm, making this one of the most well characterized samples of nearby star formation. We extend this work with a large survey imaging 283 protostars in Orion with the Hubble Space Telescope, enabling us to observe with 80 AU resolution at 1.6 µm. At this wavelength, light from the central photosphere is scattered off the dust ubiquitous throughout the gas, resolving the structure of the protostellar envelope. We use the high angular resolution to perform a morphological study of the nearby protostellar gas (the envelope), finding that our morphologies are indicative of evolutionary trends. The high resolution of this data makes it uniquely suited for finding unambiguously edge-on protostars (of which we report thirteen at high confidence) and for tracing the structure of cavities cleared by protostellar outflows. We report on one of these unambiguously edge-on protostars, HOPS 171, which we've studied in detail with the Atacama Large Millimeter/submillimeter Array to find a complex structure. We use an edge detection routine to perform the analysis on tracing cavities caused by outflows, and report the first application of such a routine to study the role of feedback on the envelope. Using evolutionary diagnostics, we find no evidence for the growth of these outflow cavities as protostars evolve through the first 1 (open full item for complete abstract)

Committee: S. Thomas Megeath (Committee Chair); Rupali Chandar (Committee Member); Steve Federman (Committee Member); Stella Offner (Committee Member); Nikolas Podraza (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2018, Astronomy

The technological advances of the recent years have allowed for the proliferation of relatively inexpensive charge-coupled devices (CCDs) and other imaging hardware that has revolutionized modern astronomy. The burgeoning field of transient astronomy is perhaps the largest benefactor of these advances, and as a result, high cadence, all-sky surveys are becoming a reality. New transient phenomena are discovered and studied in depth on a regular basis, and the datasets of ``normal'' transients are becoming richer by the day. However, transient phenomena are intimately connected to their environment, and understanding this connection can provide insight that the study of transient phenomenology alone cannot. In this dissertation, I leverage the statistical power of modern all-sky surveys to investigate the nature of transients, the properties of their host galaxies, as well as the techniques and tools we use to study both.

Committee: Krzysztof Stanek (Advisor); Christopher Kochanek (Committee Member); Paul Martini (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy (PhD), Ohio University, 2007, Physics (Arts and Sciences)

We present an analysis of star formation, cooling, and feedback in 61 galaxies at the cores of galaxy clusters. A subsample of 33 of these systems possesses cavities in the intracluster medium (ICM) inflated by radio jets emanating from their active galactic nuclei (AGN). We present an extensive analysis of the X-ray cavities in these systems. We find that AGN, through their cavities alone, are energetically able to balance radiative losses (cooling) from the ICM in more than half of these systems. Using the cavity (jet) powers, we place strong lower limits on the rate of growth of supermassive black holes in central galaxies, and we find that they are growing at an average rate of ~ 0.1 M sumyr -1, with some systems growing as quickly as ~ 1 M sunyr -1. We find a trend between bulge growth (star formation) and black hole growth that is approximately in accordance with the slope of the local (Magorrian) relation between black hole and bulge mass. However, the large scatter in the trend suggests that bulges and black holes do not always grow in lock step. With the exception of the rapidly accreting supercavity systems (e.g, MS 0735.6+7421), the black holes are accreting well below their Eddington rates. Most systems could be powered by Bondi accretion from the hot ICM, provided the central gas density increases into the Bondi radius as ρ ∝ r -1. However, if the gas density profile flattens into a core, as observed in M87, Bondi accretion is unlikely to be driving the most powerful outbursts. Using a subsample of 17 systems with published star formation rates, we examine the relationship between cooling and star formation. We find that the star formation rates are approaching or are comparable to X-ray and far-UV limits on the rates of gas condensation onto the central galaxy. The remaining radiative losses could be offset by AGN feedback. The vast gulf between radiative losses and the sink of cooling material, which has been the primary objection to cooling flows, ha (open full item for complete abstract)

Committee: Brian McNamara (Advisor) Subjects: Physics, Astronomy and Astrophysics

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

The Askaryan Radio Array (ARA) is an ultra-high-energy neutrino detector located in the Dark Sector of the South Pole. Its mission is to detect neutrinos above 10 PeV by observing radio emissions generated by relativistic particle showers in glacial ice, producing a cone of Cherenkov radiation known as Askaryan radiation. This dissertation focuses on reconstructing the polarization of these emissions, a critical step for determining neutrino trajectories and identifying their astrophysical origins. Polarization reconstruction performance is evaluated using both experimental data and simulations. Measurements from the 2018 South Pole Ice Core Experiment (SPICE), which employed controlled calibration pulses with known polarization signatures, achieved a statistical resolution of 2.7 degrees, finding agreement upon a previously reported statistical resolution of 2.7 degrees by the ARIANNA collaboration. Idealized simulations further demonstrate sub-degree resolution, highlighting the impact of noise, ice properties, and hardware limitations in real-world conditions. Additionally, an analysis of birefringence in South Pole ice introduces corrections for polarization angle rotations due to anisotropic refractive index variations, offering a path to improving reconstruction fidelity. This work represents a significant step in the development of radio-based neutrino detectors, advancing ARA's capabilities and setting benchmarks for future experiments. By improving the precision of neutrino trajectory reconstructions, these findings contribute to the broader goals of ultra-high-energy neutrino astronomy and multi-messenger astrophysics.

Committee: Amy Connolly (Advisor); Chris Hirata (Committee Member); Andrew Heckler (Committee Member); James Beatty (Committee Member) Subjects: Astronomy; Astrophysics; Particle Physics; Physics

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1964, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1964, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1970, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 1969, Graduate School

Committee: Not Provided (Other) Subjects:

Doctor of Philosophy, The Ohio State University, 2023, Astronomy

The chemical composition of the universe is constantly changing. With only hydrogen, helium, and trace amounts of lithium left over in the wake of the Big Bang, all heavier atomic nuclei in the universe were produced through the fusion of lighter nuclei inside stars. When a star dies, it disperses a considerable portion of this material back to its surroundings. As the sites of star formation in the universe, galaxies are like petri dishes of their own nuclear reactions, facilitating the formation of new stars and retaining the heavy nuclei they produce. By analyzing the chemical abundance structure of galaxies, we can deduce both their evolutionary histories and the stellar evolution processes which produced the stable elements on the periodic table. Thanks to the advent of large spectroscopic surveys, this field of galactic archaeology has recently ushered in a new age. The APOGEE survey alone has estimated abundances of at least 15 different elements in over 650,000 stars in the Galaxy. In this dissertation, I draw on galactic chemical evolution (GCE) models to shed light not only the processes shaping galaxy evolution, but also the mechanisms of nucleosynthesis in stars. Using a powerful and efficient GCE software developed as part of this work, I quantify the impact of sudden bursts in star formation in dwarf galaxies and develop methods with which to pin down the details of these events and the evolutionary timescales at play. Introducing elemental yields as free parameters, I demonstrate that this framework can deduce the evolutionary histories of galaxies and yields from stellar populations simultaneously. Applications of this methodology to disrupted dwarf galaxies in the Milky Way's stellar halo observed with the H3 survey provide results consistent with known trends of galaxy properties with stellar mass. To harness the constraining power of supernova surveys in GCE models, I investigate the origin of the observed high Type Ia supernova rates in (open full item for complete abstract)

Committee: David Weinberg (Advisor); Christopher Kochanek (Committee Member); Jennifer Johnson (Committee Member) Subjects: Astronomy; Astrophysics

Master of Sciences, Case Western Reserve University, 2023, Physics

Future Stage IV ground based CMB telescopes will be more sensitive than ever due to the increase in number of detectors and advancements in detector technology. These detectors will improve the precision and sensitivity of CMB measurements that continue to provide data on the early Universe and structure of the cosmos. Despite the increase in detector sensitivity, noise will continue to remain a problem in data extraction due to various environmental factors. Many ground based CMB experimental sites reside in high elevation, cold areas as they reduce the noise in the atmosphere that the photons travel through. In this thesis we will be looking at the best projected frequency band center and edge locations for Stage III CMB experiments at these sites, as well as deciding what changes may be made to bandwidth and edge placement in future Stage IV instruments.

Committee: John Ruhl (Advisor); Corbin Covault (Committee Member); Benjamin Monreal (Committee Member) Subjects: Astronomy; Astrophysics; Physics

Doctor of Philosophy, Case Western Reserve University, 2023, Astronomy

In this thesis, I present a series of in-depth studies on the nearby spiral galaxy M101 and its group environment. The M101 Group is a dynamic group, and thus it contains features both secular and tidal in origin: M101 is believed to have undergone an interaction with its most massive satellite NGC 5474 approximately \SI{300}{\mega\year} ago. Each study utilized deep, wide-field, narrowband imaging from the Burrell Schmidt telescope targeting the emission lines of Hα, Hβ, [OIII]λλ4959,5007, and [OII]λλ3726,3729. Searching for collisional evidence of this interaction, I present a study of the group environment of M101 and its satellites. I find that there is no large population of outlying, intragroup HII regions down to extremely low Hα flux levels. Only two sources, one associated with NGC 5474 and another associated with the background galaxy NGC 5486 were found. The former is likely an outlying HII region, while the latter is likely a background dwarf galaxy. Turning towards the disks of the M101 Group galaxies, I analyze the oxygen abundances of M101 and its two primary satellites NGC 5477 and NGC 5474. M101 shows a strong abundance gradient, while the two satellites present little or no gradient. There is some evidence of a flat gradient in M101 beyond R~15 kpc as well as azimuthal abundance variations to the west and southwest. These are likely caused by the tidal interaction in combination with the internal dynamical effects of the corotation barrier. Finally, using absorption signatures in the same narrowband images, I present constraints on the stellar ages of M101's disk and interpret these in the context of spiral wave patterns. In the inner disk, I find that stellar ages get progressively older with distance through a spiral arm, consistent with a quasi-steady spiral pattern. In the outer disk, there is a significantly young stellar population, likely the outcome of the tidal interaction with NGC 5474. In total, this thesis shows that wea (open full item for complete abstract)

Committee: Christopher Mihos (Committee Chair); Stacy McGaugh (Committee Member); Bill Janesh (Committee Member); Paul Harding (Committee Member); Steve Hauck (Committee Member) Subjects: Astronomy

Doctor of Philosophy, The Ohio State University, 2022, Astronomy

Everything around us is made up of material created by the stars. Whether formed over stars' lifetimes or through their explosive death, supernovae, a combination of stellar processes, known as nucleosynthesis, produce the elements. To decode the history and evolution of our Galaxy we must first understand the implications of its current abundances. This dissertation places observational and theoretical constraints on the origin of the elements and use these results to deduce aspects of Galactic chemical evolution, formation, and enrichment events. The last decade has seen huge advancements in large scales observations of stellar spectra, leading to catalogs of >20 elemental abundances for hundreds of thousands of stars. Surveys allow us to study population abundance trends, compare abundances in different regions of the Galaxy, and identify chemically interesting stars. Through two-process decomposition we can infer the relative contribution of CCSN and SNIa to a given element based off of its abundance trends. In my dissertation, I analyze GALAH DR2 stellar abundances to determine the fractional contribution of CCSN to the production of over 20 elements. Of note, I find that O is almost purely produced in CCSN; Si, Ca, and Al have substantial, but non-dominant SNIa production; and Fe-peak elements are dominated by SNIa production. I add empirical constraints for 9 new elements to the literature. I leverage the wide Galactic coverage of the APOGEE survey to determine the spacial homogeneity of the Galactic abundance trends. New southern hemisphere observations allow for the comparison of stellar abundances in the Milky Way disk to those in the Galactic bulge. I find small to insignificant difference between the median trends of the bulge and disk, leading to the conclusion that the relative contributions of CCSN and SNIa to the production of the elements are consistent throughout the Galaxy and that the median abundance trends are insensitive to most aspects (open full item for complete abstract)

Committee: Jennifer Johnson (Advisor); David Weinberg (Advisor); Todd Thompson (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2022, Astronomy

Galaxy formation and evolution are driven by stars and star formation. Star formation is fundamental for shaping the universe as we see it today as part of the cosmic ecosystems encompassing galaxies, yet half of the physics that determines how much gas forms into stars – the stellar feedback (injection of energy and momentum to the surrounding material) half of the tug-of-war between gravity and stellar feedback – have only recently become a focus for observational astronomers. Theoretical explorations of stellar feedback have been extensive for the past four decades and our current understanding of star-forming galaxies comes primarily through extensive modeling and simulations with sub-grid physics prescriptions based on a handful of observations. In order to secure the basis for these sub-grid physics models and expand our understanding of star-formation and the effects of massive stars during all epochs of the universe, more observations of these processes are needed. Observations of star forming regions provide the foundation to anchor simulations and observations of analogues to high-redshift galaxies help determine the sources that reionized the universe and the role stars played in during the Epoch of Reionization. With multiwavelength observations of H ii regions in the Milky Way, I have probed the effects of stellar feedback in dynamics of H ii regions, providing the necessary basis for defining the sub-grid physics in simulations. With multiwavelength observations of nearby galaxies with properties similar to galaxies in the EoR (low mass: < 107 M⊙; low metallicity: < 0.15 Z⊙; and high star-formation rates: > 10−1.2 M⊙/yr), I have determined the properties of sources that produce the photoionization feedback we observe and which sources ionized the universe in the Reionization Era. With X-ray observations of a massive colliding wind binary I have explored the effects of stellar wind feedback on small spatial scales and found that wind prescriptions assum (open full item for complete abstract)

Committee: Laura Lopez (Advisor); Todd Thompson (Committee Member); Adam Leroy (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2022, Astronomy

While the Universe might at first appear static and unchanging to a casual observer, it is teeming with variable sources and cataclysmic events that mark the births, lives, and deaths of the many and varied objects filling our Universe. In recent years, modern time-domain surveys have revolutionized the study of stellar variability by providing access to time series data for millions of stars in the Milky Way. The All-Sky Automated Survey for SuperNovae (ASAS-SN) monitors the entire visible sky daily using 20 robotic telescopes in Hawaii, Texas, Chile, and South Africa. In addition to the real-time detection of bright supernovae and other transients, archival ASAS-SN data allows for the time series characterization of over 100 million stars. By analyzing the ASAS-SN time series data for ~61 million stars, I made the first homogeneous all-sky catalog of bright variable stars and then uniformly classified them using machine learning techniques. This catalog includes the discovery of ~220,000 new variable stars and ~660,000 variables in total. I present studies that use this catalog combined with information from large scale spectroscopic surveys to study various populations of variable stars. Finally, I present examples of the discovery of rare and unusual variable stars using ASAS-SN, including the most extreme 'heartbeat'' star ever discovered.

Committee: Krzysztof Stanek (Advisor); Todd Thompson (Committee Member); Christopher Kochanek (Advisor) Subjects: Astronomy; Astrophysics; Physics

BA, Oberlin College, 2022, Physics and Astronomy

In this thesis, I introduce a method to identify and characterize the effects of active galactic nuclei (AGN) on the spectra of nearby star-forming regions. I analyze spatially-resolved areas of galaxies called “spaxels” within Data Release 15 of the Sloan Digital Sky Survey (SDSS) with the goal of locating those which are physically close to AGN. I find those spaxels with calculated metallicities which lie adjacent to AGN-flagged spaxels and characterize their metallicity values relative to the spaxels which are not adjacent to AGN-flagged spaxels, using a total of 11 separate metallicity calibrations. I find that the current methods to mask AGN-influenced regions for large-scale investigation are, in general, robust, as the largest median deviation between metallicities in border spaxels and those in non-border spaxels is 0.0467 dex. The largest mean difference in metallicity between border and non-border spaxels is 0.0522 dex with a standard deviation of 0.0590 dex. However, on a spaxel-by spaxel basis, I find that the differences in metallicity between border spaxels and non-border spaxels can be as large as 0.9350 dex. These results are concerning for spaxel-by-spaxel analysis, and indicate the need for an improved masking process in the future.

Committee: Jillian Scudder (Advisor) Subjects: Astronomy; Astrophysics; Physics

Master of Science in Computer Engineering, University of Dayton, 2022, Electrical and Computer Engineering

Automated monitoring of low resolution, deep-space objects in wide field of view (WFOV) imaging systems is an important and emerging technology for Space Domain Awareness (SDA). SDA involves the holistic process of monitoring and characterizing space objects in order to ensure a safe environment for satellite operations and employment. With the proliferation of satellites, referred to as ‘Resident Space Objects' (RSOs), in all orbits, SDA requires WFOV optical sensors to detect and track the growing population of multiple low-light objects. The PANDORA sensor array, located in Maui at the Air Force Maui Optical and Supercomputing Site, is an exemplar of a scalable imaging architecture that can detect dim deep- space objects while maintaining a WFOV. The PANDORA system captures 20◦×120◦ images of the night sky oriented along the GEO belt at a rate of two frames per minute. The PANDORA sensor system makes possible the passive monitoring of hundreds of RSOs, but requires advanced image processing and exploitation techniques to autonomously and reliably be utilized. This thesis explores image processing and deep learning techniques to exploit PANDORA sensor data for use in SDA. To benchmark object detection performance, a synthetic dataset and annotated physical dataset of PANDORA imagery is prepared. Classical feature- based object detections are explored, which are tailored to specific space object morphologies in PANDORA imagery. Single frame object detection performance with developed classical methods are evaluated on the synthetic PANDORA dataset. Deep learning object detection techniques are then employed, which set a standard for WFOV low-resolution object detection. We present a deep learning RSO detection and tracking architecture: PASTOR (Persistent All- Sky Tracking and Object Re-Identification). This architecture consists of a deep-learned object detector using YOLOv5, with an object tracker consisting of Kalman filters. We present detailed analysis o (open full item for complete abstract)

Committee: Vijayan Asari (Advisor) Subjects: Computer Engineering; Computer Science