Enhanced atomic gas fractions in recently merged galaxies: quenching is not a result of post-merger gas exhaustion
Abstract
We present a detailed assessment of the global atomic hydrogen gas fraction (fgas = log[M_{H I}/M⋆]) in a sample of post-merger galaxies identified in the Sloan Digital Sky Survey (SDSS). Archival H I measurements of 47 targets are combined with new Arecibo observations of a further 51 galaxies. The stellar mass range of the post-merger sample, our observing strategy, detection thresholds and data analysis procedures replicate those of the extended GALEX Arecibo SDSS Survey (xGASS) which can therefore be used as a control sample. Our principal results are (1) the post-merger sample shows a ∼50 per cent higher H I detection fraction compared with xGASS; (2) accounting for non-detections, the median atomic gas fraction of the post-merger sample is larger than the control sample by 0.3-0.6 dex; and (3) the median atomic gas fraction enhancement (Δfgas), computed on a galaxy-by-galaxy basis at fixed stellar mass, is 0.51 dex. Our results demonstrate that recently merged galaxies are typically a factor of ∼3 more H I rich than control galaxies of the same M⋆. If the control sample is additionally matched in star formation rate, the median H I excess is reduced to Δfgas = 0.2 dex, showing that the enhanced atomic gas fractions in post-mergers are not purely a reflection of changes in star formation activity. We conclude that merger-induced starbursts and outflows do not lead to prompt quenching via exhaustion/expulsion of the galactic gas reservoirs. Instead, we propose that if star formation ceases after a merger, it is more likely due to an enhanced turbulence which renders the galaxy unable to effectively form new stars.
- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- August 2018
- DOI:
- 10.1093/mnras/sty1247
- arXiv:
- arXiv:1805.03604
- Bibcode:
- 2018MNRAS.478.3447E
- Keywords:
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- galaxies: interactions;
- galaxies: ISM;
- galaxies: peculiar;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted for publication in MNRAS