Master Thesis Defense by Lise Klungsøyr Nøland
Title: The local interstellar environment of high-redshift star-forming galaxies probed with gamma-ray bursts
Abstract: Studying the neutral hydrogen (HI) gas content in galaxies is essential for unraveling the processes which lead to their formation and evolution. Extensive HI-mapping of nearby galaxies has been performed using the 21-cm transition, but as this line is intrinsically faint, this approach is not feasible for galaxies at redshifts higher than z ≈ 0.4. We adopt the method for obtaining the [CII]-to-HI conversion factor presented in Heintz et al. (2021), which can be used to infer the HI gas mass of individual star-forming galaxies at high redshifts through absorption line measurements from bright gamma-ray burst (GRB) afterglow spectra. This approach is extended in this thesis to also obtain [OI∗]-to-HI and [OI∗∗]-to-HI conversion factors for a sample of GRB afterglows observed with the VLT/UVES spectrograph. We find that [CII]-to-HI follows the expected anti-correlation with metallicity and that [OI∗]-to-HI also shows such a dependence, although not as strong. This anti-correlation was not found for [OI∗∗]-to-HI in our sample, which appeared to be independent of metallicity. Furthermore, we estimate the [CII*]-158 μm cooling rates to find the expected phase segregation in the interstellar medium to investigate whether our GRBs probe warm or cold neutral medium.
Supervisor:
- Kasper Elm Heintz, University of Copenhagen, Niels Bohr Insitute
Censor:
- Hans Kjeldsen, Aarhus University