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, 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, 2019, Physics

Cosmic acceleration is the most surprising discovery in modern history. While the phenomenon has been proven by a plethora of cosmological observations, the underlying mechanism is still a mystery. There have been various attempts to understand the driver of cosmic acceleration in a form of "dark energy" or "modified gravity", but none of these has compelling evidence. This thesis contains my PhD research projects dedicated to find the origin of cosmic acceleration. In Chapter 2, I describe the DES-CMASS (DMASS) galaxy sample constructed from images taken from the Dark Energy Survey (DES). The sample is designed for a joint analysis of the existing BAO and RSD measurements from BOSS using the CMASS galaxy sample and a galaxy-galaxy lensing measurement from DES. We show that DMASS successfully replicates CMASS in many ways, such as by comparing galaxy bias, angular correlation functions, and redshifts. Chapter 3 describes the DES Y1 analysis for extended cosmological models focusing on modified gravity (MG), which I contributed. DES Y1 shear measurement significantly improves the existing MG constraints. We show that the resulting MG constraints are consistent with general relativity. In the latter part of the chapter, I forecast the detection of MG parameters for DMASS to demonstrate the capability of DMASS to achieve tighter constraints by cancelling galaxy bias. Finally, in Chapter 4, we study the information content of the three-dimensional galaxy correlation function and power spectrum when realistic scale cuts are applied. We find that two estimators are complementary to each other and combining the two yields small improvement for joint constraints.

Committee: Klaus Honscheid Professor (Advisor); Christopher M. Hirata Professor (Committee Member); Samir Mathur Professor (Committee Member); Richard J. Furnstahl Professor (Committee Member) Subjects: Astrophysics; Physics

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

I present an investigation into the local warm-hot gaseous environment of the Milky Way as observed through highly ionized metal absorption lines in ultraviolet and X-ray spectra. These X-ray lines (primarily OVII) had been reported at redshifts consistent with zero in previous studies of background quasars; however, it has been unclear whether this gas exists close to the Galaxy (within a few tens of kpc) or extends far out into intergalactic space, thereby comprising most of the mass in the local universe. Additionally, highly-ionized OVI high-velocity clouds (HVCs), some of which are associated with the ubiquitous extended neutral hydrogen HVCs seen around the Galaxy, had been extensively studied. However, the distance to the OVI HVCs, and their relation to the X-ray lines, remained undetermined. With three of the highest-quality Chandra grating spectra of extragalactic sources to date, a large number of z=0 absorption lines are detected; the FUSE spectra of these same objects show low- and high-velocity OVI absorption. Using advanced curve-of-growth and ionization balance analysis, limits are placed on the velocity dispersion, temperature, and density of the warm-hot gas along these lines of sight. In none of these cases can the absorption be placed conclusively at Galactic or extragalactic distances. However, in two of the three cases (Mrk 421 and Mrk 279), the observed OVI UV absorption components are found to be inconsistent with the X-ray absorber, indicating that the X-ray absorption is either extragalactic or traces a previously undiscovered Galactic component. The third sightline (PKS 2155-304) exhibits absorption with properties more similar to Mrk 421 than Mrk 279; thus, there may be more than one physical process contributing to the observed absorption along any given sightline. While the X-ray components of this research exclusively employ Chandra data, the XMM-Newton mission can in principle be used for the same purpose. XMM's effectiveness in observ (open full item for complete abstract)

Committee: Smita Mathur (Advisor) Subjects: Physics, Astronomy and Astrophysics