SQuIGG$\vec{L}$E: Ubiquitous Cool Gas Outflows with Large Mass-Loading Factors in $z\sim0.7$ Post-starburst Galaxies

Abstract: While recent James Webb Space Telescope studies have highlighted cool gas outflows as an important mechanism for rapid quenching at $z\gtrsim2$, such space-based spectroscopic samples remain limited in size. In this work, we search for and characterize cool gas outflows traced by Fe II $λλ$2586,2600 and Mg II $λλ$2796,2803 absorption in post-starburst galaxies (PSBs) at $0.5<z<0.9$, which are accessible to ground-based spectroscopy. Utilizing the SQuIGG$\vec{L}$E survey containing over 1300 PSBs, we stack spectra in bins of stellar mass, (specific) star formation rate, burst mass, burst mass fraction, and time since quenching. We observe blueshifted line centroids indicative of outflows in all stacks except the one containing galaxies that quenched more than 260 Myr ago. Outflow velocities decline with increasing time since quenching, while showing little correlation with other galaxy properties. The inferred outflows have large mass loading factors of 1 -- 120, maximum velocities above the interstellar medium escape velocities of their host galaxies, and energy and momentum fluxes exceeding those expected from the current star formation. Our results suggest that cool gas outflows are ubiquitous in intermediate-redshift PSBs and are likely relic outflows launched by previous starburst or AGN activity. These outflows have the potential to quench star formation by transporting gas into the galactic halos, consistent with outflows playing an important role in rapid quenching from intermediate to high redshift.