Ph.D. Thesis Defenses
Challenges in theoretical modeling of cosmic reionization
March 29, 2016 | ERC 576 | 1:05 PM
Alexander Kaurov

Ph.D. Committee members: Andrey Kravtsov, Hsiao-Wen Chen, Wayne Hu

"Dr. Alexander Kaurov's work on studying cosmic reionization - the process of ionization of the bulk of cosmic gas by ultraviolet radiation from the first stars and quasars - was instrumental in combining diverse theoretical concepts into a single, unified paradigm that connects directly with modern state-of-the-art numerical simulations. This breakthrough will have numerous practical applications for the analysis and interpretation of the forthcoming observational data from the future James Webb Space Telescope, Giant Magellan Telescope, and radio observations of the epoch when the first galaxies lit up."
- Nickolay Y. Gnedin, Ph.D. advisor

Thesis Abstract: As the sensitivity and precision of modern instruments increases, the observations start to approach two digit redshifts, which is a mid-reionization epoch. In the upcoming decade we expect to have many of highly diverse observations of the epoch of reionization. Those observations will include: 21cm global signal and tomography experiments, improved CMB polarization measurements, the properties of individual galaxies including Ly╬▒ emitters, and the ionization state of the IGM through observations of the spectra of high-z quasars.

Even though for each of these observations theoretical models are already developed; there is no unified theoretical framework to analyze them altogether in a self-consistent way, i.e. to perform a full Bayesian analysis of all available observations. Therefore, I would like to discuss why it is still an unsolved problem and how it can be approached. In particular, I will talk about our latest developments in numerical simulations of cosmic reionization with full radiation transfer, and their interplay with approximate semi-analytical methods. Most importantly, I will review possibilities for the parameter spaces used in reionization models. In addition, I will present our recent results on more exotic reionization scenarios that include dark matter annihilation.

Snapshots of Faraway Places: Intensive Atmosphere Characterization of Extrasolar Planets
May 24, 2016 | ERC 576 | 3:00 PM
Laura Kreidberg

Scientific Advisor: Jacob L. Bean

Ph.D. Committee members: Daniel Fabrycky, Hsiao-Wen Chen, and Andrey Kravstov

"Laura conducted the most ambitious observational programs ever on the topic of exoplanet atmospheres for her dissertation. She used large investments of Hubble and Spitzer Space Telescope time to measure exoplanet atmospheric compositions, thermal structures, energy budgets, and dynamics to understand planetary origins and physics. The papers resulting from her work are the new benchmarks in the field, and provide a foundation for studying the atmospheres of potentially habitable planets with future facilities."
- Jacob L. Bean, Ph.D. advisor

Thesis Abstract: Exoplanet atmosphere characterization has the potential to reveal the origins, nature, and even habitability of distant worlds. This thesis represents a step towards realizing that potential for a diverse group of four extrasolar planets. Here, I present the results of intensive observational campaigns with the Hubble and Spitzer Space Telescopes to study the atmospheres of the super-Earth GJ 1214b and the hot Jupiters WASP-43b, WASP-12b, and WASP-103b.

I measured an unprecedentedly precise near-infrared transmission spectrum for GJ 1214b that definitively reveals the presence of clouds in the planet's atmosphere. For WASP-43b and WASP-12b, I also measured very precise spectra that exhibit water features at high confidence (>7 sigma). The retrieved water abundance for WASP-43b extends the well-known Solar System trend of decreasing atmospheric metallicity with increasing planet mass. The detection of water for WASP-12b marks the first spectroscopic identification of a molecule in the planet's atmosphere and implies that it has solar composition, ruling out carbon-to-oxygen ratios greater than unity. For WASP-103b, I use the new technique of phase-resolved spectroscopy to determine the planet's temperature structure, dynamics, and energy budget. In addition to these observations, I also present the BATMAN code, an open-source Python package for fast and flexible modeling of transit light curves.

Taken together, these results provide a foundation for comparative planetology beyond the Solar System and the investigation of Earth-like, potentially habitable planets with future observing facilities.