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

We measure velocity offsets in the $\mathrm{NaI}\lambda\lambda5890,5896$ ($\mathrm{NaD}$ ) interstellar medium absorption lines to track how neutral galactic winds change as their host galaxies evolve. Our sample of $\sim 80,000$ 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 ($\mathrm{log}_{10}(M_{\ast}/M_{\odot}) > 10$ ). Along this sequence, the fraction of outflows decreases ($76\% \pm 2\%$ per cent to $65\% \pm 4\%$ to a $3\sigma$ upper limit of $34\%$ ), and the mean velocity offset changes from outflowing to inflowing ($-84.6 \pm 5.9\ \mathrm{km/s}$ to $-71.6 \pm 11.4\ \mathrm{km/s}$ to $+76.6 \pm 2.3\ \mathrm{km/s}$ ). 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 $1/2-\mathrm{opening\ angle} > 45^{\circ}$ ) instead of from the nucleus: the wind velocity decreases as the disc becomes more edge-on, and the outflow fraction, constant at $\sim 90\%$ for disc inclinations $i < 45^{\circ}$ , steadily decreases from $\sim 90\%$ per cent to $\sim 20\%$ for $i > 45^{\circ}$ .

Monthly Notices of the Royal Astronomical Society, Volume 528, Issue 4, pages 5783-5803