Multi-Element Abundances as Probes of Galaxy Growth Across Cosmic Time

This thesis presents a comprehensive study of multi-elemental abundances in galaxies across a wide range of stellar masses, star formation rates, and redshifts, aiming to better characterize mass-metallicity relations (MZRs) and to probe the physical processes that govern chemical enrichment in galaxies over cosmic time. Chapter 2 demonstrates that low- and high-mass stellar MZRs can be placed on a consistent absolute scale by comparing stellar metallicities from resolved and integrated-light spectroscopy in NGC 147, a Local Group dwarf galaxy. The two methods yield consistent [Fe/H] values, validating integrated-light techniques in measuring stellar metallicity in distant galaxies. In Chapter 3, I analyze deep Keck spectra of two gravitationally lensed, quiescent galaxies at z ~ 1. Both galaxies are metal-poor compared to local analogs but share comparable [Mg/Fe]. These results suggest that both galaxies experienced early, rapid star formation and strong outflows that depleted their gas reservoirs and drove early quenching. Chapter 4 introduces a new sample of 46 star-forming and 2 quiescent systems with M* = 108–1010 M☉ at z ∼ 0, observed with the Keck Cosmic Web Imager (KCWI). Combining with SDSS data, I construct the first consistently derived Fe- and Mg-MZRs from 108 to 1011.5 M*. I find that scatter in the stellar MZRs is driven by varying sSFR, with more active galaxies showing lower stellar abundances at fixed mass. This chapter also presents the first comparison of α elements (O and Mg) in stars and the ionized gas beyond the Local Group, revealing a tight [Mg/H]*–[O/H]g correlation. The finding that [O/H]g generally exceeds [Mg/H]* implies star formation is fueled by enriched, well-mixed interstellar medium rather than pristine gas inflows. Chapter 5 further explores spatially resolved nebular and stellar properties in the KCWI sample. Star-forming dwarfs exhibit clumpy star formation, diverse local ionization conditions, and smooth stellar mass profiles. Some show established gas-phase metallicity gradients, although diffuse ionized gas may bias gradient measurements. Together, these studies advance our understanding of how elemental abundances evolve across different galaxy masses and redshifts, offering new insights into the processes that regulate galaxy growth, enrichment, and quenching.