Quiescent galaxies at cosmic noon: From individual element abundances to star formation histories

Understanding the formation and early evolution of massive quiescent galaxies is crucial for a complete picture of galaxy formation in a cosmological context. Indeed, in a cold dark matter dominated Universe hierarchical galaxy formation makes it difficult to form massive galaxies quickly and preserve them in just a passive evolution state for most of the cosmic time, as suggested by studying their local fossil population. Such a comprehensive picture can be obtained through precise measurements of individual elemental abundances, which encode the timescales and physical conditions of their star-formation and assembly histories. While extensive work at low and intermediate redshift has revealed strong correlations between stellar mass, metallicity, and abundance ratios, studies at z ∼ 2 − 3 (i.e., the epoch when most progenitors of present day early-type first quenched) remain extremely limited. This is primarily due to the faintness and compactness of these systems, which make it extremely challenging to obtain medium-resolution near-infrared spectra with the quality required for a detailed chemical analysis. We present a science case to measure full elemental abundance patterns in a representative sample of massive quiescent galaxies at cosmic noon, exploiting rest-frame optical absorption features. We show that deriving robust stellar population constraints for these systems requires spectra with S/N > ∼ 20 per resolution element, together with a spatial resolution comparable to their ∼ 0.1 arcsec sizes. We show, through dedicated exposure time simulations, that such requirements can only be met with a 40m class telescope equipped with a powerful adaptive optics system. In this context, SHARP-NEXUS, in combination with MORFEO-MCAO capabilities, emerges as the only viable ELT instrument capable of enabling this science, providing both the sensitivity and angular resolution needed. Although massive quiescent galaxies are rare at these redshifts, their study can efficiently exploit the instrument’s multiplexing by targeting galaxy overdensities and coordinating with surveys of star-forming galaxies. Such synergistic strategies, proven feasible in high-redshift clusters and by multiplex-sharing facilities like 4MOST, would allow SHARP-NEXUS to open a new window on the chemical enrichment of the earliest massive galaxies.