Master Thesis Defense by Omar Ahmad Rashdan
Title: Photometric Tomography of the Intergalactic Medium at the Reionization Epoch
Abstract: The study of the intergalactic medium (IGM) and its interaction with light from distant galaxies provides crucial insights into the evolution of the Universe. In this project, we apply a technique called photometric intergalactic medium tomography to reconstruct a map of the large-scale structure of the IGM in the early Universe, at redshift 5.71, using publicly available data from the HSC and UltraVISTA cameras, along with the use of the photometric COSMOS2020 catalogue. We develop a spectral energy distribution (SED) fitting tool using Markov Chain Monte Carlo (MCMC) methods to measure the IGM transmission along a sample of photometric background galaxies, using Lyman-alpha absorption as a tracer of the IGM transmission. These measurements are then used to construct a map of the IGM during the Epoch of Reionization (EoR). We photometrically estimate the mean IGM transmission for individual galaxies, as well as the mean transmission across the selected sample. Although interloper galaxies initially posed a challenge, a color cut in the relevant filters improved the purity of the sample. We have reconstructed the first 2D tomographic map of the IGM at this redshift. While the map is inherently noisy due to the photometric nature of the data, the cross-correlation with foreground Lyman-alpha emitters (LAEs) is consistent with the theoretical expectations. Finally, we identify candidate high-transmission regions that may correspond to ionized bubbles in the IGM, potentially marking regions of early, galaxy-driven reionization. This work demonstrates the feasibility of using photometric observations to map the IGM and offers a scalable new tool for studying the end stages of cosmic reionization.
Supervisor:
- Koki Kakiichi, University of Copenhagen, Niels Bohr Institute
Censor:
- Thomas R. Greve, DTU Space
