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JWST is discovering increasing numbers of quiescent galaxies 1--2 billion years after the Big Bang, whose redshift, high mass, and old stellar ages indicate that their formation and quenching were surprisingly rapid. This fast-paced evolution seems to require that feedback from AGN (active galactic nuclei) be faster and/or more efficient than previously expected Xie24. We present deep ALMA observations of cold molecular gas (the fuel for star formation) in a massive, fast-rotating, post-starburst galaxy at z=3. 064. This galaxy hosts an AGN, driving neutral-gas outflows with a mass-outflow rate of 6020 M_ yr^-1, and has a star-formation rate of <5. 6 M_ yr^-1. Our data reveal this system to be the most distant gas-poor galaxy confirmed with direct CO observations (molecular-gas mass < 10^9. 1 M_; <0. 8 % of its stellar mass). Combining ALMA and JWST observations, we estimate the gas-consumption history of this galaxy, showing that it evolved with net zero gas inflow, i. e. , gas consumption by star formation matches the amount of gas this galaxy is missing relative to star-forming galaxies. This could arise both from preventive feedback stopping further gas inflow, which would otherwise refuel star formation or, alternatively, from fine-tuned ejective feedback matching precisely gas inflows. Our methods, applied to a larger sample, promise to disentangle ejective vs preventive feedback.
Scholtz et al. (Wed,) studied this question.