Master Thesis Defense by Isabella Henum

Title: Exploring the chemical enrichment of galaxies within 600 Myr after the Big Bang

Abstract: Throughout the last 12 Gyr of cosmic time, galaxies have been observed to follow a universal relation known as the fundamental metallicity relation (FMR), which connects the star formation rates (SFRs), stellar masses and chemical abundances of galaxies. With spectroscopic data from the James Webb Space Telescope (JWST), it is now for the first time possible to reliably measure the chemical abundances of galaxies within the first few Myr after the Big Bang, at redshifts z > 7, and investigate whether these galaxies follow the FMR. In this thesis, I will present how I first familiarize with spectroscopy, by collecting the wavelength of each visible emission line in spectroscopic observations obtained with the Multi-Object Spectrometer for Infrared Exploration (MOSFIRE). I then proceed to utilize spectroscopic data obtained with the Near-Infrared Spectrograph (NIRSpec) on the JWST to measure the gas phase oxygen abundance of two high redshift galaxies denoted RXJ_95 and SMACS_85, at redshifts z = 9.5 and z = 8.5 respectively. I determine the oxygen abundance by employing two methods: one based on the electron temperature of the ionized gas and one using empirical strong line calibrations. For both galaxies, I find that their SFRs are higher than for galaxies with similar masses in the local universe, while their oxygen abundances are lower. Although these results align with observational expectations, I also find that the oxygen abundances of the galaxies are significantly lower than predicted by the FMR, suggesting that this relation is not universal at redshifts z > 8. This may imply that high redshift galaxies are closely connected with the intergalactic medium and subject to continuous infall of metal poor gas which effectively dilutes their metal abundances in the interstellar medium.

Supervisor:

  • Victoria Bellinger Strait, University of Copenhagen, Niels Bohr Insitute

Censor:

  • Hans Kjeldsen, Aarhus University