Master Thesis Defense by Catrine Robinson Christiansen

Title: Characterization of Galaxies during the Epoch of Reionization with JWST: Using Spectroscopic and Photometric Observations alongside Galaxy Formation Simulations

Abstract: The formation and evolution of galaxies in the early universe remain key questions in modern astrophysics, particularly regarding the role of neutral hydrogen during cosmic reionization. This thesis investigates the nature of strong damped Lyman-alpha (DLA) absorption features in early galaxies, examining whether these features originate primarily from the interstellar medium (ISM) or the circumgalactic medium (CGM). By analyzing the spatial distribution and properties of neutral hydrogen in high-redshift galaxies using galaxy formation simulations, the results are compared with JWST observations to better determine the location of the gas responsible for the observed DLA features.

To address this question, an observed galaxy at z = 8.76 with a strong DLA feature is analyzed using spectroscopic data, measuring its star formation rate, metallicity, and hydrogen column density. Through a detailed line-of-sight analysis of multiple simulated galaxies spanning redshifts 5.5 to 10, this study quantifies the probability of measuring high-column-density neutral gas and investigates its dependence on our viewing angle and the galaxy stellar mass and redshift.

The results indicate that the majority of the neutral hydrogen responsible for DLA absorption is located within the ISM of the central galaxy rather than the CGM. The probability of observing high HI column densities significantly decreases when the central 0.5-1 kpc of the galaxy is excluded from the analysis. Furthermore, while stellar mass correlates with higher column densities in the CGM, no clear redshift dependence is observed within the simulated sample. These results suggest that early galaxies contain substantial neutral gas reservoirs.

Supervisor:

  • Kasper Elm Heintz, University of Copenhagen, Niels Bohr Institute

Co-Supervisor:

  • Viola Gelli, University of Copenhagen, Niels Bohr Institute

Censor:

  • Frank Grundahl, Aarhus University