Proefschrift
Chronicles of Cosmic Dawn
This thesis investigates the interplay between high-redshift quasars and the intergalactic medium (IGM) during the Epoch of Reionization (EoR). It combines new observations, systematic measurements, and forward modeling to constrain the physical state of hydrogen in the early Universe.
- Auteur
- S. Onorato
- Datum
- 13 november 2025
- Links
- Thesis in Leiden Repository
Chapter 2 presents a homogeneous spectroscopic dataset of 45 quasars at 6.5<7.65, uniformly reduced with PypeIt and used to construct composite rest-frame UV spectra. These composites reveal remarkable consistency in quasar spectral slopes and emission-line properties across cosmic time, suggesting little evolution in their broad UV characteristics.
Chapter 3 measures proximity-zone sizes for 59 quasars (5.76<7.55), showing that their luminosity dependence agrees with photoionization expectations, while the redshift evolution is steeper than previously reported. The large scatter in proximity zones reflects variations in quasar lifetime, environment, and IGM neutral fraction, with some objects likely representing extremely young quasars.
Chapter 4 introduces a forward-modeling framework comparing observed Ly-alpha transmission PDFs with simulations from Nyx and 21cmFAST. The results highlight good agreement within proximity zones but significant tension in the Ly-alpha forest, pointing to missing physics such as patchy reionization or UV-background fluctuations.
Together, these studies refine our understanding of how quasars illuminate the evolving IGM near the end of reionization.