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, 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, Case Western Reserve University, 2018, Astronomy

To investigate the growth and evolution of the earliest structures in the Universe, we identify more than 200 galaxy overdensities in the Candidate Cluster and Protocluster Cat- alog (CCPC). This compilation is produced by mining open astronomy data sets for over- densities of high redshift galaxies that are spectroscopically confirmed. At these redshifts, the Universe is only a few billion years old. This data mining approach yields a nearly ten fold increase in the number of known protoclusters in the literature. The CCPC also includes the highest redshift, spectroscopically confirmed protocluster at z = 6.56. For nearly 1500 galaxies contained in the CCPC between redshifts of 2.0 < z < 6.6, we find archival Spitzer images at 3.6 and 4.5 µm bandpasses. These Spitzer wavelengths serve as a proxy measurement for the stellar mass of the galaxies. The galaxies in protoclusters appear to be consistent with a passively evolving, older stellar population. We find no sta- tistically significant difference between protocluster and field galaxy populations. Galaxy formation models suggest that galaxies in dense environments should be more massive. Comparing the brightness distribution of the data at different epochs provides an evolution- ary track for how protocluster galaxies evolve. We compare the data to the predictions of a large-scale simulation, the Millennium Run. We analyze the simulated data with the same suite of algorithms and metrics as in the CCPC. The results of this exercise yield a number of significant discrepancies between the theoretical predictions and what is seen. The universe contains a much larger density of bright galaxies than what the model predicts. At z > 2, the brightest galaxies are older and more massive than anticipated by the model.

Committee: Stacy McGaugh (Advisor) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, Case Western Reserve University, 2017, Astronomy

In this dissertation, I present a series of studies on the low surface brightness outskirts of galaxies, which contain a record of tidal interactions and secular evolution processes. Each study utilized new deep imaging from the Burrell Schmidt Telescope in either broadband filters or narrow-band filters targeting Halpha emission. Regarding tidal interactions, I present a study of the M96 Group (or Leo I Group), as well as deep imaging of the interacting pair M51. I find that the M96 Group's intragroup light (IGL) consists of only three faint linear streams. I find no stellar counterpart to the group's H I ring, unusual if it were collisional in origin, and few signs of interaction among its four most massive members, implying a very calm tidal history. In M51, I discover several extremely diffuse plumes of starlight, yet find no stellar counterpart to its H I tail. Additionally, I measure red (B - V ~ 0.8) colors in all of its most extended tidal features, implying dominantly old populations and thus a lack of interaction-induced extended star formation. Regarding secular evolution, I conduct a detailed photometric study of three nearby galaxies' outer disks. Each outer disk lacks both ongoing star formation and the spiral structure necessary to migrate stars from the inner disk, hence it is unclear how these red outer disks formed. Finally, I conduct a study of the H II regions and diffuse ionized gas (DIG) throughout the M101 Group, to determine whether star formation in low density environments occupies a distinct physical regime from its high density counterpart. I find that the distribution of Halpha/FUV flux ratios (a tracer of the initial mass function, IMF) is constant among all H II region populations throughout the group. Also, the Halpha/FUV ratio in the DIG appears tied only to the local intensity of star formation, leaving little room for changing star formation physics. In total, this dissertation shows that tidal interactions in low-density (open full item for complete abstract)

Committee: J. Christopher Mihos (Advisor); Paul Harding (Committee Member); Stacy McGaugh (Committee Member); Heather Morrison (Committee Member); Steven Hauck Jr. (Committee Member) Subjects: Astronomy

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

The standard Λ Cold Dark Matter (ΛCDM) model assumes that our Universe is geometrically flat and expanding, governed by General Relativity, and made up of three main constituents at present: baryonic matter, dark matter, and dark energy. Within the last decade the parameters governing ΛCDM have been tightly constrained by a variety of cosmological measurements including those of the cosmic microwave background (CMB), baryon acoustic oscillations (BAO), galaxy clustering, weak gravitational lensing, and redshift space distortions (RSD). Despite the impressive ability of ΛCDM to describe these varied observations substantial challenges to the model remain. In particular there remains a 5-10% tension between predictions of matter clustering from CMB data and other, late-time cosmological probes. The resolution of this tension may ultimately lie in new physics, such as complex dark energy or dark matter, or a deviation from General Relativity on cosmological scales. Establishing or refuting the reality of this tension is therefore one of the highest priority challenges of observational cosmology today. In this dissertation I present research on a variety of topics within cosmology related to meeting this challenge. The primary focus of my research is to derive robust and precise constraints on ΛCDM using novel combinations of cosmological observables that utilize galaxy clusters. I also present research on halo and galaxy assembly bias. Both of these phenomena are related to my primary research focus because they can potentially bias cosmological constraints. Finally I present work on modeling and forecasting the combination of galaxy-galaxy lensing and galaxy clustering in the final data release of the Dark Energy Survey. Much of the technical development in this work will be applicable to my primary research focus in the future. Beginning in Chapter 1 we study halo assembly bias for haloes in the mass range 3.7 × 1011 h-1 Msun - 5.0 ×1013 h-1 Msun. Using the Lar (open full item for complete abstract)

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

Doctor of Philosophy, The Ohio State University, 2015, Physics

The Dark Energy Survey (DES) is an ongoing cosmological survey intended to study the properties of the accelerated expansion of the Universe. In this dissertation, I present work of mine that has advanced the progress of DES. First is an introduction, which explores the physics of the cosmos, as well as how DES intends to probe it. Attention is given to developing the theoretical framework cosmologists use to describe the Universe, and to explaining observational evidence which has furnished our current conception of the cosmos. Emphasis is placed on the dark sector – dark matter and dark energy – the content of the Universe not explained by the Standard Model of particle physics. As its name suggests, the Dark Energy Survey has been specially designed to measure the properties of dark energy. DES will use a combination of galaxy cluster, weak gravitational lensing, angular clustering, and supernovae measurements to derive its state of the art constraints, each of which is discussed in the text. The work described in this dissertation includes science measurements directly related to the first three of these probes. The dissertation presents my contributions to the readout and control system of the Dark Energy Camera (DECam); the name of this software is SISPI. SISPI uses client-server and publish-subscribe communication patterns to coordinate and command actions among the many hardware components of DECam – the survey instrument for DES, a 570 megapixel CCD camera, mounted at prime focus of the Blanco 4-m Telescope. The SISPI work I discuss includes coding applications for DECam's filter changer mechanism and hexapod, as well as developing the Scripts Editor, a GUI application for DECam users to edit and export observing sequence SISPI can load and execute. Next, the dissertation describes the processing of early DES data, which I contributed. This furnished the data products used in the first-completed DES science analysis, and contributed to improving th (open full item for complete abstract)

Committee: Klaus Honscheid (Advisor) Subjects: Astronomy; Astrophysics; Physics

Doctor of Philosophy, University of Toledo, 2015, Physics

Most stars form in groups and clusters. Stars clusters range in age from very young (< 3 Myr, embedded in gas clouds) to some of the most ancient objects in the universe (>13 Gyr), providing clues to the formation and evolution of their host galaxies. Our knowledge of the diversity of star cluster populations has expanded over the last few decades, especially by being able to examine star clusters outside of the Milky Way (MW). In this dissertation, we continue this expansion of extragalactic star cluster studies by examining the star cluster system of the nearby spiral galaxy M101. We utilize photometry from Hubble Space Telescope images to assess luminosity, color, size, and spatial distributions of old star clusters, and spectroscopy from the Gemini-North telescope to determine ages, metallicities, and velocities of a subset of both young and old clusters in M101. We find that the range of cluster luminosities, ages, and metallicities in M101 is nearly continuous. We discover a population of fairly massive, old disk clusters, and conclude that the disk of M101 may have had a higher rate of cluster formation in the past than in the MW, and that it may be better suited to cluster survival. We find evidence that some clusters in M101 have intermediate ages of several Gyr, whereas the MW has few such clusters. Our analysis of the velocities of young clusters suggests that they rotate with the HI gas disk, while the old globular clusters appear to be in the halo.

Committee: Rupali Chandar (Committee Chair); John-David Smith (Committee Member); Steven Federman (Committee Member); Bo Gao (Committee Member); Bradley Whitmore (Committee Member) Subjects: Astronomy; Astrophysics; Physics

Doctor of Philosophy, The Ohio State University, 2014, Astronomy

Elemental abundances of gas and stars are sensitive diagnostics of the main processes that drive galaxy evolution: gas inflow, star formation, enrichment, and gas outflow. The relation between galaxy stellar mass and gas-phase oxygen abundance, known as the mass-metallicity relation (MZR), is one of the strongest constraints on galaxy evolution models. However, the popular strong line methods of measuring oxygen abundance have large systematic uncertainties. We employ a more robust direct method to measure the metallicities of ~200,000 star-forming galaxies from the Sloan Digital Sky Survey stacked in bins of stellar mass and star formation rate (SFR) to significantly enhance the signal-to-noise ratio of the weak auroral lines required for the direct method. The direct method MZR has a steeper slope, a lower turnover mass, and a factor of 2-3 greater dependence on the SFR than strong line MZRs. Gas-phase abundances reflect a galaxy's current abundances, but stellar abundances encode its complete enrichment history. We use a sample of 35 microlensed bulge dwarf and subgiant stars, whose brightness increased by a factor of 100-1000 due to lensing from an intervening star, to investigate the formation of the Galactic bulge. We apply principal component abundance analysis (PCAA)---a principal component decomposition of relative abundances [X/Fe]---to this sample to characterize its distribution in the 12-dimensional space defined by their elemental abundances. The first principal component PC1, which describes the abundance patterns of most stars in the sample, shows a strong contribution from alpha-elements, reflecting the relative contributions of core-collapse and Type Ia supernovae. The second principal component PC2 is characterized by a Na-Ni correlation, the likely product of metallicity-dependent core-collapse supernova (CCSN) yields. Applying PCAA to a sample of local disk dwarfs yields a nearly identical PC1, suggesting br (open full item for complete abstract)

Committee: David Weinberg (Advisor); Jennifer Johnson (Committee Member); Marc Pinsonneault (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2013, Astronomy

The accelerated expansion of the Universe can be explained by either the cosmological constant Λ, a repulsive dark energy, or modifications to General Relativity (GR) on cosmological scales. The key to distinguishing these possibilities is to study the growth of large-scale structures over cosmic time, measured primarily by three methods: cosmic shear from weak lensing (WL), redshift-distortion (RSD) of galaxy clustering, and the traditional cluster cosmology using the abundance of galaxy clusters as function of mass. Although cosmic shear and RSD are commonly studied using galaxies, the two effects are much more enhanced around galaxy clusters. In this dissertation, I develop novel yet powerful techniques to combine cluster WL, galaxy infall kinematics, and cluster abundances to derive constraints on cosmological models and test of modified gravity (MG) theories. One of the main systematical uncertainties of cluster cosmology is in cluster mass calibration. Common mass observables, including galaxy richness, X-ray luminosity, and Sunyaev-Zel'dovich (SZ) decrements, correlate with cluster true mass with some scatter. Using MaxBCG cluster catalog derived from the Sloan Digital Sky Survey (SDSS) and assuming Λ-Cold Dark Matter (ΛCDM) model, I developed an alternative method for constraining cosmological parameters, i.e., the matter density Ωm and the clustering amplitude ς8, while simultaneously calibrating the scatter in the richness-mass relation, by combining the abundance of clusters as function of richness and the large-scale cluster WL profiles. We find ς8(Ωm/0.325)0.501=0.828±0.049, consistent with constraints from other MaxBCG studies that use WL measurements on small scales. The (Ωm,ς8) constraint is consistent with and orthogonal to the one inferred from WMAP CMB data, reflecting agreement with the structure growth predicted by General Relativity for a ΛCDM cosmological model. A joint constraint assuming ΛCDM yields Ωm=0.298-0.020+0.019 and ς8=0.831-0 (open full item for complete abstract)

Committee: David Weinberg (Advisor); Christopher Kochanek (Committee Member); Todd Thompson (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2011, Astronomy

In this dissertation, I use cosmological hydrodynamic simulations to study galaxy growth and the relationship between dark matter halos and the galaxies that form in them. We use cosmological SPH simulations to study galaxy growth and the relationship between dark matter halos and the galaxies that form in them. We find that the distinction between central and satellite galaxies in our simulation is weaker than expected in simple models where only central galaxies are able to accrete mass and ‘receive' mergers of less massive systems. Instead, in our simulation, satellite galaxies continue to accrete gas and convert it to stars after halo mergers with a larger parent halo. Satellites in our simulation are 0.1-0.2 magnitudes bluer than in models that assume no gas accretion on to satellites after a halo merger (instantaneous ‘strangulation'), which is sufficient to shift galaxies across the boundary from the ‘red sequence' to the ‘blue cloud'. Subhalo abundance matching (SHAM) is a technique for assigning luminosities to simulated dark matter substructures by assuming a strictly monotonic relationship between luminosity and halo mass at the epoch of accretion. We carry out N-body and SPH simulations of a cosmological volume with identical initial conditions, finding that SHAM successfully matches the stellar masses and luminosities of SPH galaxies at a wide range of epochs, albeit with relatively small amounts of scatter. In our SPH simulations that include momentum driven winds, the results are more complex. In order to guide efforts to fit star formation histories to observed colours or spectra, we investigate parametric fits to the star formation histories of SPH galaxies finding that some commonly used models fail to describe the star formation histories of SPH galaxies and introduce significant errors in estimates of physical parameters of galaxies, but other simple parameteric models achieve greater success.

Committee: David Weinberg Dr (Advisor); Chris Kochanek Dr (Committee Member); Todd Thompson Dr (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

Two fundamental predictions of modern cosmological models are that i) galaxies form from small perturbations in the cosmic density field and ii) there is a tenuous medium between the galaxies that traces the underlying dark matter distribution in a relatively simple way. This thesis concerns the structure of the intergalactic medium (IGM) and its relation to galaxies. Specifically, I analyze the nature of the IGM, observable via the Lyman-alpha transition of hydrogen, as predicted from cosmological hydrodynamic simulations of a cold dark matter + dark energy universe. I first quantify the relation between galaxies and absorption in the Lyman-alpha forest on large (~10 Megaparsec) and small (~0.5 Megaparsec) scales and show that, in the absence of feedback from the galaxies themselves, observations of this relation can serve as robust tests of the inflationary cold dark matter model. I show that the strong bias of high redshift galaxies toward high density regions imprints a clear signature on the distribution of flux in the Lyman-alpha forest, and these predictions are examined as functions of galaxy baryon mass, star formation rate, and dark matter halo mass and occupation. I then investigate the potential impact of galaxies on the IGM and find that supernova-driven winds (as predicted in cosmological simulations) can substantially impact their local surroundings, particularly via heating, but that only very powerful winds can create easily detectable “holes” in the IGM. The impact of winds on the Lyman-alpha optical depth near galaxies is less dramatic than their impact on gas temperature because winds heat only a small fraction of the gas present in the turnaround regions surrounding galaxies, all of which contribute to the Lyman-alpha forest near galaxies. Finally, I combine a Monte Carlo radiative transfer code with cosmological hydrodynamic simulations to investigate the signature of fluorescent Lyman-alpha emission from large scale structure due to impinging (open full item for complete abstract)

Committee: David Weinberg (Advisor) Subjects: Physics, Astronomy and Astrophysics

BA, Oberlin College, 2009, Physics and Astronomy

This thesis discusses research being done to understand the inner parts of the Milky Way Galaxy. We already know that there are dense star clouds, a supermassive black hole, and a large bar structure, but much of the inner galaxy is shrouded in mystery. Dust absorption, for one thing, prevents us from seeing the galactic center directly with our eyes. To help understand the elusive inner Milky Way, we examine radio telescope data taken in Antarctica by Oberlin College Professor Chris Martin. His gigahertz radio observations were already analyzed to help understand how gas funnels into the Milky Way's supermassive black hole. We study this data further to characterize turbulence and predict how hot or cold the gas is. The analysis of this data will also help prepare for the next thing: Herschel Space Observatory. This European telescope is scheduled to be launched in late April and will begin taking data in the fall of 2009. Chris Martin was granted 125 hours of observation time on the telescope to study the Inner Milky Way.

Committee: Chris Martin PhD (Advisor) Subjects: Astrophysics

Bachelor of Science (BS), Ohio University, 2013, Astrophysics

Hypervelocity stars (HVSs) are thought to be produced via three-body interactions between a binary star system and a supermassive black hole. HVSs are powerful tools studying the structure of the Galactic dark matter halo, and the mass function and population of stars near the Galactic Center. To date, there are 21 known HVSs, almost all of which are assumed to be massive early-type (OBA) main sequence stars. Current detection methods are unable to find low-mass, solar-type HVSs. We use a new method for finding solar-type HVSs which selects candidates on the basis of their proper motions, requiring their velocity vectors to be consistent with an origin in the Galactic Center. Using intermediate-resolution optical spectra for 115 potential HVSs, we measure the three-dimensional galactic rest-frame velocity and position. We have identified 10 strong HVS candidates whose galactic rest-frame velocity is larger than 400 km/s and total velocity vector is consistent with galactocentric origin and 50 candidates whose galactic rest-frame velocity is larger than 400 km/s. Follow-up observations of these candidates are necessary to confirm their distance, and total velocity vector. We have shown it is possible to search for low-mass HVSs using a proper motion survey and Advancements in photometry, astrometry and distance measurements, like the GAIA mission, will pave the way for similar surveys

Committee: Doglas Clowe Dr. (Advisor); Adam Kraus Dr. (Other) Subjects: Astronomy; Astrophysics

Bachelor of Sciences, Ohio University, 2010, Physics and Astronomy

Finding a new way to measure distances to galaxy clusters would allow current cosmological models to be tested and/or constrained. We propose to accomplish this by using a distance indicator that was investigated by Postman and Lauer (1995). They used a relationship discovered by Hoessel (1980) that compares the metric luminosity, within the inner 10 h-1 kpc, of a brightest cluster galaxy (BCG) to the logarithmic slope of its surface brightness profile (α = d log L / d log r). Postman and Lauer proved that this relationship did provide a standard candle based on BCG's for distances to a redshift of z ~ 0.05. With new data from the HST, we now have images of much more distant galaxy clusters than ever before (z~1). With this data, we can test to see if the relationship holds true over much larger distances. A problem that is always present within this work is the process of deciding how much light comes from the actual galaxy and how much comes from nearby galaxies. We use a program called GALFIT (Peng 2009) to fit the galaxies and remove the light that comes from objects other than the BCG within the cluster's core. This provides an even clearer look into the galaxy cluster, allowing our measurements to be that much more precise. Using images from the HST ACS provided in the ESO Distant Cluster Surver (EdisCS), we have reduced data for ten different clusters. Of the original ten, alpha parameters could be found for seven of these clusters. We also got alpha values for 12 additional clusters from the HST Archive Galaxy-Scale Gravitational Lens Survey (HAGGLeS). We used the exact same equation that Postman and Lauer created to fit their data, simply adjusting the intercept to account for our F814W bandpass. Our best χ2 fit is of the form: Mm = -20.809 – 4.397α + 2.738α2. This fit increases the scatter of the magnitudes from 0.198 mag (intrinsic) to 0.270 mag (corrected). A possible redshift-α relation was found to exist and warrents more investi (open full item for complete abstract)

Committee: Douglas Clowe PhD (Advisor) Subjects: Astronomy; Astrophysics; Physics

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

Self-interacting dark matter (SIDM) cosmologies admit an enormous diversity of dark matter (DM) halo density profiles, from low-density cores to high-density core-collapsed cusps. The possibility of the growth of high central density in low-mass halos, accelerated if halos are subhalos of larger systems, has intriguing consequences for small-scale observables such as substructure lensing, dwarf galaxies and stellar streams. However, following the evolution of low-mass subhalos in their host systems is computationally expensive, sometimes even prohibitive, with traditional N-body cosmological simulations. In this thesis work, we are thus motivated to develop a series of hybrid methods for simulations of low-mass subhalos, from core-creation to core-collapse (or complete dissolution in the host), also with the orbital effects from the host halo consistently captured. This thesis consists of three parts: in the first chapter, we detail our hybrid method tracing individual SIDM subhalos; in the second chapter, we use the hybrid method to simulate a realistic population of subhalos, also with a new hierarchical framework to further reduce the computational cost; in the third chapter, we populate individual SIDM subhalos with galaxies in the initial condition, and study the evolution of stellar properties in response to SIDM halo evolution and orbital effects.

Committee: Annika Peter (Advisor); Paul Martini (Committee Member); Samir Mathur (Committee Member); John Beacom (Committee Member) Subjects: Astrophysics; Physics

Doctor of Philosophy (PhD), Ohio University, 2024, Physics and Astronomy (Arts and Sciences)

As more wide-angle, large-scale, all-sky surveys become available so do opportunities for significant advancements into our understanding of the Universe through the study of formation and evolution of structure and testing cosmological models. It is important to address the systematic errors of weak lensing measurements as statistical errors improve, especially those that are planned as part of an automated process such as pipelines for the Vera Rubin Observatory's Legacy Survey of Space and Time. I obtained and analyzed images from 14 Hubble Space Telescope Advanced Camera for Surveys Wide Field Camera galaxy clusters spanning redshifts from 0.4 to 0.9 to identify potential galaxy cluster centroids and determine the optimal centroid usage based on observable indicators. I utilized the Principal Component Analysis method on individual exposures to describe the point spread function and the KSB+ method to correct the galaxy shapes and measure the shear. I then performed a bootstrap resampling analysis to identify the weak lensing centroid for each cluster. I compared this centroid with the brightest cluster galaxy (BCG), light and X-ray centroids to determine which centroid was optimal. I also searched for observable markers indicating when it is beneficial to use which centroid. My analysis of the survey suggests the BCG as the better choice of center compared to light or X-ray centroids, but is still offset from the mass centroid at a statistically significant level in a number of the clusters. I found no clear indicator within my research of an ideal centroid choice.

Committee: Douglas Clowe (Advisor); Joseph Shields (Committee Member); Ryan Fogt (Committee Member); David Drabold (Committee Member); Eric Stinaff (Committee Member) Subjects: Astronomy; Astrophysics; Physics

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

Low-mass galaxies provide an exciting opportunity to learn about many open questions in astronomy, including topics as seemingly disparate as galaxy formation and evolution and the particle nature of dark matter. To take full advantage of these galaxies however, we must devote energy to understanding the basics about their mass and environment. Traditionally this requires distance measurements that use expensive space-based imaging or spectra. An alternative approach is to exploit the discrete nature of galaxy stellar populations to measure so called surface brightness fluctuations (SBF), which change as a function of distance. SBF can provide accurate distances to galaxies without the stringent observational requirements necessary for other distance techniques and often without the need for extensive follow-up data after discovery. Given the huge number of low-mass galaxies being discovered in recent surveys and the upcoming deep imaging observatories that will undoubtedly uncover even more such galaxies, SBF offers a promising solution to obtaining distances to a revolutionary sample of these fascinating systems. In this dissertation, I develop an image processing pipeline with the goal of measuring SBF distances to dwarf galaxies with the Large Binocular Telescope. First, I demonstrate the technique with a quenched galaxy called Blobby in the outskirts of the M81 group. I use the measured distance to argue that Blobby is part of an understudied population of galaxies called backsplash galaxies, and that its mass and stellar population have likely been significantly affected by a past interaction with the group. Next, I measure the SBF of several other Local Volume galaxies, some with widely respected tip of the red giant branch (TRGB) distance measurements. I demonstrate that SBF is competitive with other distance methods and confirm (or reject) associations of dwarfs in the sample with several host galaxies. I discuss challenges with the SBF method, particula (open full item for complete abstract)

Committee: Annika Peter (Advisor); Klaus Honscheid (Committee Member); Linda Carpenter (Committee Member); Todd Thompson (Committee Member) Subjects: Astronomy; Astrophysics; Physics

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

The Dark Energy Spectroscopic Instrument (DESI) is a purpose built instrument on the Mayall 4-meter telescope in Kitt Peak, Arizona. It is undertaking an ambitious, 5 year survey of the same name to measure the redshifts of 40 million galaxies and quasars. At the time of writing DESI is about 2 years into its 5 year survey. With the vast new dataset collected by DESI, the DESI collaboration will produce novel constraints on cosmology and in particular the nature of dark energy using techniques such as Baryon Acoustic Oscillations and Redshift Space Distortions. In this work I detail some of my contributions to the success of DESI as a survey. These include in particular the design and writing of software for the Focal Plane System and its novel robotic fiber positioners as well as the commissioning of the Focal Plane system and continued support in the early survey. This does not include earlier work on testing and verifying positioner robots off of the production line. This document will also cover an exploration into a new method to account for systematics in clustering measurements resulting from the DESI instrument. The chapters will proceed as follows. The first chapter will provide a brief introduction to our cosmological universe, concluding with its statistical fluctuations and how we measure the fluctuations. The second chapter will introduce the DESI instrument, the survey it is undertaking and its key operational loop. The third chapter will cover the development of the focal plane software used through commissioning, its structure, and will conclude with some performance statistics. The fourth chapter will cover the commissioning of the focal plane, challenges encountered and key moments. The fifth and final chapter will discuss the imputation of galaxies into DESI clustering catalogs, this is an exploration into a potential new way to account for systematics resulting from the design of DESI and its survey.

Committee: Klaus Honscheid (Advisor); Paul Martini (Committee Member); Christopher Hirata (Committee Member); Richard Furnstahl (Committee Member) Subjects: Astrophysics; Physics

Master of Science (MS), Ohio University, 2023, Physics and Astronomy (Arts and Sciences)

Baryon Acoustic Oscillations (BAO) are sound waves in the photon-baryon fluid that was the early universe, frozen at the surface of last scattering as the universe expanded and cooled. The signatures of these waves show up in the Cosmic Microwave Background as well as large-scale galaxy distribution, and because of this they have a known scale length. Thus, BAO can be used to determine the expansion history of the universe, with the ultimate goal of constraining the density of dark energy as a means of revealing its nature. The Nancy Grace Roman Space Telescope (Roman) is a telescope set to launch in 2027. It will be performing a large spectroscopic survey, mock catalogs of which are now available. This work uses these mock catalogs to examine the BAO signature present in the 2-point correlation function of galaxy distribution in order to predict how well the BAO peak can be recovered from the survey's galaxy redshift data. We tested different expected survey conditions, finding that the BAO feature in the correlation function can be recovered to within one standard deviation in comparison to a reference cosmological model, and is a worthwhile goal for the Roman telescope galaxy survey.

Committee: Hee-Jong Seo (Advisor); Christian Drischler (Committee Member); Douglas Clowe (Committee Chair) Subjects: Astronomy

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