Quenching of Star Formation in Massive Galaxies

Abstract

The shutdown of star formation—quenching—marks a pivotal transition in the lives of massive galaxies, which dominate the present-day stellar mass density. This review synthesizes our current understanding of the mechanisms that trigger and maintain quiescence. We discuss the nuances of how quiescent systems are identified across cosmic time and summarize the evolving physical properties of the growing massive population, including their stellar populations, chemical enrichment histories, and gas and dust reservoirs, highlighting several key results: ▪ Quiescent galaxies can be identified with empirical color selections, but evolving specific star-formation rate thresholds offer a more robust physical distinction from star-forming systems. ▪ The earliest massive quiescent stellar populations show rapid formation histories and high metallicities, with enhanced α-elemental abundances often distinct from local analogs. ▪ Nascent studies of gas and dust in quiescent galaxies reveal diverse multiphase reservoirs and outflows, pointing to fast ejective and slow regulatory modes of galaxy quenching. ▪ In situ processes establish galaxy central density while assembly continues via (minor) mergers postquenching, reshaping all massive galaxies and disrupting rotation in most cases. We distill observations into two broad modes by which massive galaxies form and quench: One involves a rapid, early shutdown driven by supermassive black hole outflows on short timescales; the other proceeds gradually through gas exhaustion, virial heating, or preventative feedback, each leaving distinct observational signatures. Together, these pathways offer a testable framework for modeling the formation and evolution of massive galaxies, which will be informed by future studies of their stars, gas, dust, and dynamics.