Tracing the evolution of the molecular gas content in galaxies is critical for a complete understanding of galaxy formation and evolution, as it provides the direct fuel for star formation. Studies... Show moreTracing the evolution of the molecular gas content in galaxies is critical for a complete understanding of galaxy formation and evolution, as it provides the direct fuel for star formation. Studies of high-redshift (z>1) molecular gas reservoirs, most commonly traced by carbon monoxide (CO), have seen substantial growth in recent years thanks to state-of the-art sub-millimeter interferometers such as the Jansky Very Large Array or the Atacama Large Millimeter Array. However, these studies have been largely based on detections of the bright mid/high-J transitions of CO (J>=3), which have been shown to give a biased and incomplete view of the total cold molecular gas content in galaxies. This thesis presents an observational study of the cold interstellar medium of massive galaxies in the distant universe. Chapter 2 presents one of the highest—resolution studies of low-J CO in a high—redshift galaxy to-date, allowing us to map its total cold gas reservoir in unprecedented detail. Chapter 3 presents a survey targeting low-J CO emission in high-redshift unobscured quasar hosts, finding direct evidence for high gas fractions but very short depletion times. Chapter 4 introduces first results from the VLA Legacy Library of Molecular Gas at High Redshift project, which significantly expands the number of high-redshift galaxies with cold gas detections. Finally, Chapter 5 shows ALMA observations targeting emission from atomic carbon in a subset of the VLA targets, and demonstrates how this alternative gas tracer complements our view of cold molecular gas reservoirs at high—redshift. Show less
Frias Castillo, M.; Hodge, J.A.; Rybak, M.; Werf, P.P. van der; Smail, I.; Birkin, J.E.; ... ; Dannerbauer, H. 2023
The formation and evolution of galaxies is fundamentally driven by the formation of new stars out of cold gas. Observations of young stars in distant galaxies in the early universe, such as we can... Show moreThe formation and evolution of galaxies is fundamentally driven by the formation of new stars out of cold gas. Observations of young stars in distant galaxies in the early universe, such as we can see in the Hubble Ultra Deep Field, have unveiled how the cosmic star formation rate density evolves. Yet, while the effect of star formation—the young stars—has been mapped in ever-increasing detail, the cause—the cold molecular gas that fuels star formation—has been elusive. This thesis presents an observational study of the cold interstellar medium of distant galaxies in the early universe, using the most sensitive submillimeter telescope to date, the Atacama Large Millimeter Array, together with new integral-field spectrographs, such as the Multi Unit Spectroscopic Explorer on the Very Large Telescope. It unveils the physical properties of star-forming galaxies and their molecular gas reservoirs, and describes the evolution of the cosmic molecular gas density—the fuel for star formation. Show less
In this thesis, I study the extreme environment of galaxy centers by understanding the conditions of the the molecular gas; the fuel of star formation. The fundamentals of star formation can be... Show moreIn this thesis, I study the extreme environment of galaxy centers by understanding the conditions of the the molecular gas; the fuel of star formation. The fundamentals of star formation can be understood as a balance between the available molecular gas supply and feedback processes. By observing transitions of molecular and atomic species, I have determined the mechanisms that are heating the gas, the gas density, radiation environment, and mass. Show less