  Post-starburst galaxies are sources that had the last major episode of star
formation about 1 Gyr before the epoch of the observations and are on their way
to quiescence. It is important to study such galaxies at redshift z > 1, during
their main quenching phase, and estimate their molecular gas content to
constrain the processes responsible for the cessation of star formation. We
present CO(3-2) ALMA observations of two massive (Mstar ~ 5 x 10^10 Msun)
post-starburst galaxies at z > 1. We measure their molecular gas fraction to be
f_H2 = M_H2/Mstar ~ 8% - 16%, consistent with z < 1 post-starburst galaxies
from the literature. The star formation efficiency of our targets is ~ 10x
lower than that of star-forming galaxies at similar redshift, and they are
outliers of the f_H2 - specific star formation rate (sSFR) relation of
star-forming galaxies, as they have larger f_H2 than expected given their sSFR.
The gas fraction of post-starbursts from our sample and the literature
correlates with the Dn4000 spectral index, a proxy of the stellar population
age. This suggests that their gas content decreases after the last major burst
of star formation. Finally, one of our targets is undergoing a major merger
phase with two highly star-forming companions. This hints at a picture where a
perturber event (e.g., major merger) quenches star formation without completely
removing the molecular gas.
