Scholte, Dirk; (2024) Tracing galaxy evolution through stars, metals, gas and dark matter in the DESI survey. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In this thesis we use the first year of observations from the Dark Energy Spectroscopic Instrument (DESI) Survey to gain new insights into galaxy evolution. DESI is measuring the optical spectra of 40 million galaxies during a 5 year survey that started in June 2021. We study the key building blocks of galaxies and the processes that connect them using the unprecedented number of DESI spectra. To study the role of gas in galaxy evolution we develop photoionisation models that allow us to derive reliable gas mass measurements from the optical spectroscopy. This method allows us to derive gas masses for vast numbers of galaxies that are inaccessible to direct methods. We use these measurements to show that gas is a fundamental driver of the scatter in the mass-metallicity relation. The scaling relations that connect different galaxy properties are mostly well understood for massive galaxies, however, this is not the case in the dwarf galaxy regime. Therefore, we combine DESI with the Arecibo Legacy Fast ALFA (ALFALFA) blind HI survey to create the only large representative sample of galaxies with direct atomic gas mass measurements covering this entire mass range. We constrain the atomic gas sequence and mass-metallicity relation from dwarfs (10⁶ Msun) to massive galaxies (10¹¹⁻⁵ Msun). Lastly, we study the dependence of the stellar mass-to-halo mass relation on galaxy properties. We measure the dark matter distribution (DS) around star forming and quiescent galaxies using weak gravitational lensing. We combine DESI with the Hyper Suprime-Cam (HSC), Kilo-Degree Survey (KiDS) and Dark Energy Survey (DES) background galaxy shape catalogs to derive exceptionally high signal-to-noise DS measurements. We use these results to show that the bimodality in the dark matter halo masses of star forming and quiescent galaxies may not be as strong as previously implied. The work in this thesis demonstrates the value of DESI for galaxy evolution studies using the first year of observations. The full survey promises to transform our understanding of galaxy formation and evolution in these key areas.

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