Evolution of gas flows along the starburst to post-starburst to quiescent galaxy sequence

We measure velocity offsets in the Na I λλ5890, 5896 (Na D) interstellar medium absorption lines to track how neutral galactic winds change as their host galaxies evolve. Our sample of ∼80 000 SDSS spectra at 0.010 < z < 0.325 includes starburst, post-starburst, and quiescent galaxies, forming an evolutionary sequence of declining star formation rate (SFR). We detect bulk flows across this sequence, mostly at higher host stellar masses (log(M_∗/M_☉)) > 10). Along this sequence, the fraction of outflows decreases (76 ± 2 per cent to 65 ± 4 per cent to a 3σ upper limit of 34 per cent), and the mean velocity offset changes from outflowing to inflowing (−84.6 ± 5.9 to −71.6 ± 11.4 to 76.6 ± 2.3 kms⁻¹). Even within the post-starburst sample, wind speed decreases with time elapsed since the starburst ended. These results reveal that outflows diminish as galaxies age. For post-starbursts, there is evidence for an AGN contribution, especially to the speediest outflows: (1) SFR declines faster in time than outflow velocity, a decoupling arguing against massive stellar feedback; (2) of the few outflows strong enough to escape the interstellar medium (9/105), three of the four hosts with measured emission lines are Seyfert galaxies. For discy starburst galaxies, however, the trends suggest flows out of the stellar disc plane (with outflow 1/2-opening angle > 45^◦) instead of from the nucleus: the wind velocity decreases as the disc becomes more edge-on, and the outflow fraction, constant at ∼ 90 per cent for disc inclinations i < 45^◦, steadily decreases from ∼ 90 per cent to 20 per cent for i > 45^◦,.