UC Berkeley

Massive galaxies are fundamental to our understanding of cosmic history, yet the physical processes that governed their rapid assembly and quenching remain incompletely understood. This thesis presents a comprehensive, multi-epoch investigation of the chemical compositions of massive quiescent galaxies across cosmic time, combining full-spectrum fitting of large spectroscopic surveys—including SDSS and LEGA-C—with new observations with the Keck Telescopes and JWST.At intermediate redshift (z ∼ 0.7), we measure Mg and Fe abundances for a representative sample of quiescent galaxies, demonstrating robust correlations between stellar compactness as traced by M∗/Re, age, and metallicity, and showing that younger, more compact galaxies exhibit higher [Mg/H] and [Fe/H]. Extending these measurements to a broader suite of elements, we find that multi-element abundance patterns are most strongly governed by stellar velocity dispersion. At higher redshift (z ≳ 1), with the Keck Heavy Metal Survey, we identify galaxies with depleted iron and elevated [Mg/Fe], signatures of short, intense star-formation histories not seen in the local universe. These trends are inconsistent with pure minor-merger-driven evolution, suggesting a key role for major mergers or centrally rejuvenated star formation in shaping the massive quiescent population.JWST observations enable abundance measurements for an expanded range of elements at z = 1–3, revealing that the earliest quiescent galaxies are markedly Fe-poor and carbon-deficient. This result is consistent with extremely rapid star formation and quenching, preceding significant enrichment from Type Ia supernovae and asymptotic giant branch (AGB) stars. Chemically inferred star-formation timescales are found to be up to six times shorter than those derived from traditional spectral fitting, emphasizing the diagnostic power of detailed abundance analysis.To interpret these data, we introduce a new chemical evolution framework that applies empirically calibrated, IMF-averaged, metallicity-dependent yields from Milky Way disk stars. This model successfully reproduces observed multi-element abundance patterns from z ∼ 0 to z ∼ 2 with typical offsets of just 0.06 dex. Furthermore, we show that the abundances of most elements can be accurately predicted using only Mg and Fe, revealing highly regular chemical enrichment pathways in massive galaxies. This finding provides a straightforward and efficient framework for incorporating detailed abundance predictions into stellar population models, and paves the way for using chemical abundances to probe the high-mass end of the stellar initial mass function in massive galaxies.Together, this thesis charts the evolution of massive quiescent galaxies across cosmic time, establishing detailed chemical abundances as essential tracers of their rapid formation and quenching, and introducing a new framework that provides deeper insight into the physical mechanisms that shape them.