2025ApJ...993..158S

Recent observations at low redshift have revealed that some post-starburst galaxies retain significant molecular gas reservoirs despite low ongoing star formation rates, challenging most theoretical predictions that rely on heating or expelling gas reservoirs to shut down star formation. To test whether this finding holds during the peak epoch of quenching, here we present Atacama Large Millimeter/submillimeter Array CO(2-1) observations of five spectroscopically confirmed massive post-starburst galaxies at z ∼ 1.4 from the HeavyMetal survey. While four galaxies are undetected in CO emission, we detect ${M}_{{{\rm{H}}}_{2}}\sim 1{0}^{9.7}\,{M}_{\odot }$ of molecular gas in one system. The detected system is a close pair of two massive (M_* = 10^11.1–11.2M_⊙) post-starburst galaxies with no clear tidal features, likely caught in the early stages of a major merger. These results suggest that mergers may be a key factor in retaining molecular gas while simultaneously suppressing star formation in quenched galaxies at high redshift, possibly by driving increased turbulence that decreases star formation efficiency. Our nondetected galaxies have postburst ages >200 Myr, consistent with results at z < 1; however, our gas-rich post-starburst pair is significantly older than typical gas-rich quenched systems at low redshift. Our results highlight the importance of major mergers in shaping the cold gas content of quiescent galaxies during the peak epoch of quenching.