Enhanced atomic gas fractions in recently merged galaxies: quenching is
  not a result of post-merger gas exhaustion
  We present a detailed assessment of the global atomic hydrogen gas fraction
in a sample of post-merger galaxies identified in the Sloan Digital Sky Survey
(SDSS). Archival HI 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 HI 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; 3) The median atomic gas fraction enhancement (delta fgas),
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 HI rich than control galaxies of the same M*. If the control sample is
additionally matched in star formation rate, the median HI excess is reduced to
delta fgas = 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.
