Cosmic dust plays a crucial role in the evolution of galaxies. It absorbs and re-radiates the light from stars and galaxies, altering the light that we observe. Half of the metals in the interstellar medium (ISM) of galaxies are incorporated into dust. Acting as a coolant, cosmic dust is necessary for the formation of stars and is a catalyst for the production of molecules. Therefore, cosmic dust affects the overall chemical enrichment of the ISM. One of the most effective ways to study the chemical composition of the ISM is through absorption-line spectroscopy. This powerful method allows us to probe the gas-phase abundances of various metals and determine how much of these metals are locked up in dust grains, a phenomenon called dust depletion. By characterizing dust depletion across different galactic environments, we can gain valuable insights into the origin, composition, and evolution of cosmic dust. Understanding dust depletion enables a more in depth study of the ISM chemical properties, with broader implications on galaxy evolution.
My PhD has primarily focused on characterizing dust depletion across a wide range of galactic environments, from the Milky Way to distant galaxies, and investigating the properties of cosmic dust. I collected ISM metal column density measurements from the literature and complemented these with new column density measurements of titanium and nickel, which I performed using Voigt-profile fitting, on 70 damped Lyman-α absorbers (DLAs) towards quasars (QSOs). This allowed me to characterize the dust depletion of 18 metals, using the relative abundances of metals, in the Milky Way, the Magellanic Clouds, DLAs towards QSOs and towards gamma-ray bursts (GRBs). The results of this work have strong implications on the origin of cosmic dust and the dust production mechanisms. Motivated by these findings, I conducted a follow-up study to investigate further the dust properties in these samples. We developed a novel method to determine the dust-to-metal (DTM) and dust-to-gas (DTG) ratios, dust composition, and extinction using dust depletion. These results have strong implications on the dust and metal content of different galaxies up to z = 6.3. My contribution to the dust depletion scheme, has impacted several other studies on the dust and metal content of galaxies, including the investigation of chemical diversity of gas in distant galaxies, the dust and metal content in the environment of GRB afterglows and the characterization of α-element enhancement in local and distant galaxies. Finally, we developed a novel method to characterize dust depletion, using observed correlations between the relative abundances of 17 metals in diverse galactic environments. This unified method offers a new approach in the characterization of dust depletion, which supersedes the previous schemes and is valuable for understanding the chemical evolution of galaxies across cosmic time. The continued study of cosmic dust and dust depletion will bring us closer to a compre- hensive understanding of galaxy evolution. By refining our methods for dust depletion, and by applying these to even more distant and diverse galaxies, we can unveil the processes that shape the chemical makeup of the universe over cosmic time.
