Evolution of gas flows along the starburst to post-starburst to quiescent galaxy sequence
Abstract
We measure velocity offsets in the $\rm{Na {}\rm {\small I}}$ λλ5890, 5896 ($\rm{Na {}\rm {\small D}}$) 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 $76.6\pm 2.3\, \rm km s^{-1}$). 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 $\sim 90~{{\ \rm per\ cent}}$ for disc inclinations i < 45°, steadily decreases from $\sim 90~{{\ \rm per\ cent}}$ to 20 per cent for i > 45°.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2024
- DOI:
- 10.1093/mnras/stae366
- arXiv:
- arXiv:2310.00424
- Bibcode:
- 2024MNRAS.528.5783S
- Keywords:
-
- ISM: jets and outflows - ISM: kinematics and dynamics - galaxies: evolution - galaxies: ISM;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 22 pages, 19 figures, accepted for publication in MNRAS