Carbon and Iron Deficiencies in Quiescent Galaxies at <i>z</i> = 1–3 from JWST-SUSPENSE: Implications for the Formation Histories of Massive Galaxies

Abstract We present the stellar metallicities and multielement abundances (C, Mg, Si, Ca, Ti, Cr, and Fe) of 15 massive (log M / M ⊙ = 10.2–11.2) quiescent galaxies at z = 1–3, derived from ultradeep JWST-SUSPENSE spectra. Compared to quiescent galaxies at z ∼ 0, these galaxies exhibit a deficiency of 0.26 ± 0.04 dex in [C/H], 0.16 ± 0.03 dex in [Fe/H], and 0.07 ± 0.04 dex in [Mg/H], implying rapid formation and quenching before significant enrichment from asymptotic giant branch stars and Type Ia supernovae. Additionally, we find that galaxies forming at higher redshift consistently show higher [Mg/Fe] and lower [Fe/H] and [Mg/H], regardless of their observed redshift. The evolution in [Fe/H] and [C/H] is therefore primarily driven by lower-redshift samples naturally including galaxies with longer star formation timescales. In contrast, the lower [Mg/H] likely reflects earlier-forming galaxies expelling larger gas reservoirs during their quenching phase. Consequently, the mass–metallicity relation, primarily reflecting [Mg/H], is somewhat lower at z = 1–3 compared to the lower-redshift relation. Finally, we compare our results to standard stellar population modeling approaches employing solar abundance patterns and nonparametric star formation histories (using Prospector ). Our simple stellar population (SSP)-equivalent ages agree with the mass-weighted ages from Prospector , while the metallicities disagree significantly. Nonetheless, the metallicities better reflect [Fe/H] than total [ Z /H]. We also find that the star formation timescales inferred from elemental abundances are significantly shorter than those from Prospector , and we discuss the resulting implications for the early formation of massive galaxies.