Doctor of Philosophy, The Ohio State University, 1968, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1957, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

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, 1969, Graduate School

Committee: Not Provided (Other) Subjects:

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

BA, Oberlin College, 2018, Physics and Astronomy

In this thesis, I discuss the creation of a simulation that attempts to reconstruct secondary spectra of pulsars by simulating the scattering in the interstellar medium. For the simulation, we focus on two distinct scattering phenomena, namely a coherent deflection at grazing incidence along a sheet of material, and a random deflection due to a random-walk type process through clouds of material. The simulation focuses on a representation known as a Wavefield Representation that our group has not utilized to this extent before, and it allowed us to understand the physics behind these scattering events in new depths. The final product allows us to explore a number of unique scenarios involving random scattering as well as coherent screens, which is extremely interesting and potentially beneficial to our work. Going forward, we intend to expand the versatility of the simulation to try to fully reconstruct spectra like ones that we observed in our work on the Green Bank Telescope Scintarc Survey that my partner Lele Mathis and I conducted together.

Committee: D.R. Stinebring (Advisor) Subjects: Astrophysics; Physics

Doctor of Philosophy, The Ohio State University, 1969, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 1968, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

MS, University of Cincinnati, 2001, Arts and Sciences : Physics

Radio astronomy is the science of collecting extra-terrestrial radiation in the range of 15 MHz to 600 GHz to gain understanding of celestial objects. In this thesis I discuss both the single parabolic reflector radio telescope and the two-telescope radio interferometer used in radio astronomy. The total power received by a parabolic reflector is dependent on the size of the antenna, the efficiency of the reflector, the wavelength of light under observation, and the angular response of the antenna, called the "normalized power pattern". Diffraction effects limit the resolution of the single parabolic reflector. The two-telescope interferometer has increased resolution because the main beam that would be created by a single antenna is split into multiple beams through interference, with the width of one beam corresponding to the angular resolution of the interferometer. A commonly used typed of interferometer is the correlating interferometer that integrates the product of the voltages received at each telescope. The correlating interferometer does not measure the received power directly, but rather the Fourier transform of it called the visibility function. By taking many measurements with different baselines, the visibility function can be sampled over the Fourier transform (or u-v plane) space. The visibility function can then be inverted to create a radio map of the brightness distribution of the source.

Committee: Randy Johnson (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy (PhD), Ohio University, 2006, Physics (Arts and Sciences)

We have been studying extra-planar neutral hydrogen (HI) in the disk-halo transition of the inner Galaxy with the Green Bank Telescope (GBT) and the Very Large Array (VLA) of the National Radio Astronomy Observatory (NRAO). The main results of this study are 1) the discovery of a huge superbubble, whose top lags behind the rotation of the Milky Way, and 2) increased understanding of the nature of halo clouds. The study revealed a huge superbubble centered around longitude ≈ 30°, extending above the Galactic plane to latitudes >25° at a distance of about 7 kpc. It is detected in both HI and Hα. Using the GBT, we have measured more than 220,000 HI spectra at 9' angular resolution in and around this structure. The total HI mass in the system is about a million M Sunand it has an equal mass in H +. From a Kompaneets model we estimate that the age of this system is ≈ 30 Myr and its total energy content ~ 10 53ergs. Both observational and theoretical evidence suggests that the shell is now undergoing significant instabilities. The top of the superbubble (located at z ≈ 3.4 kpc) contains 3 x 10 4M Sunof HI and appears to be dominated by Galactic rotation, but with a lag of 27 km s -1from corotation. We offer a model that may explain this lag. Much of extra-planar HI in the inner Milky Way is organized into cloud-like structures not related to the classic high-velocity clouds. They are found to distances >2 kpc from the plane and can contain hundreds of M Sunof HI. Many of these clouds are parts of the superbubble possibly revealing their origin: turbulent decomposition of supershells. Twenty clouds were observed in 21cm emission with the VLA at 1' resolution, revealing their internal structure. Several of the clouds were also observed in HI absorption against background continuum sources with the VLA and the Giant Metrewave Radio Telescope (GMRT) to measure their opacity and spin temperature. These results indicate that the clouds may contain little turbulence.

Committee: Felix Lockman (Advisor) Subjects: Physics, Astronomy and Astrophysics