Galaxies through cosmic time illuminated by gamma-ray bursts and quasars
In the early Universe, most of the cold neutral gas that will later form into individual stars and galaxies is practically invisible to us. These neutral gas reservoirs can, however, be illuminated by bright cosmic lightsources such as gamma-ray bursts (GRBs) and quasars. The aim of this thesis is to use these luminous objects as tools to study the environments of intervening or host galaxy absorption systems through cosmic time. Part I is dedicated to examining the gas, dust and metals in the immediate region surrounding GRBs. Part II presents a search for and the study of cold and molecular gas in high-z GRB host galaxy absorption systems. Part III focuses on using quasars to examine gas-rich intervening galaxies in the line of sight, with specific focus on absorption systems rich in dust and metals. This thesis demonstrates the importance of observing large samples of GRB afterglows to 1) allow for statistical studies of the GRB phenomena itself and the associated host galaxy environments and 2) to obtain spectra of peculiar or unusual GRB afterglows, that is only observed rarely. In addition, it highlights that defining a complete and unbiased sample of quasars is vital to fully exploit the potential of quasars as probes of cosmic chemical evolution. In this version of the thesis only the title, author list and abstract for each published paper, presented as individual chapters, are provided. Principal supervisor: Prof. P\'all Jakobsson.