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

Recent James Webb Space Telescope studies have highlighted cool gas outflows as an important mechanism for rapid quenching at z ≳ 2, but such space-based spectroscopic samples remain limited in size. This work searches for and characterizes cool gas outflows traced by Fe II 2586,2600 and Mg II 2796,2803 absorption in post-starburst galaxies (PSBs) at 0.5 < z < 0.9, which are accessible to ground-based spectroscopy.

Using the SQuIGGLE survey containing over 1300 PSBs, the authors stack spectra in bins of stellar mass, (specific) star formation rate, burst mass, burst mass fraction, and time since quenching.

They 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 current star formation.

These results suggest that cool gas outflows are ubiquitous in intermediate-redshift PSBs and are likely relic outflows launched by previous starburst or AGN activity. Such outflows have the potential to quench star formation by transporting gas into galactic halos, consistent with outflows playing an important role in rapid quenching from intermediate to high redshift.