Probing the Dynamics and Metal Content of Galactic Winds Through Absorption and Emission Lines
Galactic winds, or galaxy-scale outflows of gas, not only shape many observable properties of the galaxy population but also play a crucial role in the evolution of the universe. They are ubiquitously detected in multi-wavelength observations over cosmic time and found driven by different physical sources, such as the core-collapse supernovae, active galactic nuclei, and cosmic rays. Theorists found cosmological models would overproduce stellar mass and star formation rates (SFR) from comic noon to the present without proper treatment of galactic winds. Through these simulations, galactic winds also determine the overall shape and amplitude of the relations between galaxies’ observable properties, such as the mass-metallicity relation (MZR), and regulate the escape of Lyman continuum photons. Despite these discoveries from detecting and simulating galactic winds, we only have a surface understanding of how winds transport mass, momentum, energy, and metal to larger galaxy radii or even the circumgalactic medium due to the lack of interface study that can connect theoretical models to observational work. In this proposal, the investigators aim to investigate the radial structure in supernovae-driven winds through absorption and emission lines to quantify the mass, momentum, energy, and metal outflow rates. With this investigation, the investigators will be able to determine the dynamics of galactic winds and the chemical evolution of galaxies. To achieve these goals, the investigators will (1) simulate emission and absorption lines from an appropriate galactic wind model that considers the radiative cooling function or the hydrodynamic mixing mechanism between the hot and cold phases of outflows. The model that succeeds in reproducing the observed absorption and emission line profiles in the cold phase of outflows, which are available from the archival HST/COS spectra and new proposed Keck/ESI spectra, will then be applied to determine the dynamics of galactic winds. Complementary to these 1D spectra, the investigators will (2) use Keck/KCWI data to detect spatial variations in the emission line profiles to help us disentangle galactic wind models with many free variables so that 1D ESI spectra cannot break the degeneracy between them. The investigators will also (3) determine the gas-phase metallicity of cold-phase galactic winds for a galaxy sample with a wide range of observable quantities. With these metallicity measurements, the investigators will directly verify whether most star-forming galaxies, especially low-mass galaxies, have metal-enriched galactic winds and whether physical quantities (e.g., the outflow metallicity and the metal outflow rate) depend on the stellar mass and SFR in galaxies. The proposed project has a duration of three years.