Date of Award
Doctor of Philosophy (PhD)
Astrophysical & Planetary Sciences
J. Michael Shull
The chemical evolution of the Universe is a complicated process with countless facets that define its properties over the course of time. In the early Universe, the metal-free first stars were responsible for originally introducing metals into the pristine gas left over from the Big Bang. Once these metals became prevalent, they forever altered the thermodynamics of the Universe. Understanding precisely where these metals originated, where they end up, and the conditions they experience along the way is of great interest in the astrophysical community. In this work, I have used numerical simulations as a means of understanding two separate phenomena related to the chemical evolution the Universe.
The first topic focuses on the question as to whether or not core-collapse supernovae in the high-redshift universe are capable of being "dust factories" for the production of galactic dust. To achieve this, I carried out idealized simulations of supernova ejecta clouds being impacted by reverse-shock blast waves. By post-processing the results of these simulations, I was able to estimate the amount of dust destruction that would occur due to thermal sputtering. In the most extreme scenarios, simulated with high relative velocities between the shock and the ejecta cloud and high gas metallicities, I find complete destruction for some grains species and only 44% dust mass survival for even the most robust species. This raises the question as to whether or not high-red shift supernova can produce dust masses in sufficient excess of the ~1 Msun per event required to match observations of high-z galaxies.
The second investigation was driven by the desire to find an answer to the missing baryon problem and a curiosity as to the impact that including a full non-equilibrium treatment of ionization chemistry has on simulations of the intergalactic medium. To address these questions, I have helped to develop Dengo, a new software package for solving complex chemical networks. Once this new package was integrated into Enzo, I carried out a set of cosmological simulations that served as both a test of the new solver and a confirmation that non-equilibrium ionization chemistry produces results that are drastically different from those that assume collisional ionization equilibrium. Although my analysis of these simulations is in its early stages, I find that the observable properties of the intergalactic medium change considerably. Continued efforts to run state-of-the-art simulations of the intergalactic medium using Dengo are warranted.
Silvia, Devin W., "Investigating the Chemical Evolution of the Universe via Numerical Simulations: Supernova Dust Destruction and Non-Equilibrium Ionization Chemistry" (2013). Astrophysical & Planetary Sciences Graduate Theses & Dissertations. 23.