Molecular Gas during the Post-Starburst Phase: Low Gas Fractions in
  Green Valley Seyfert Post-Starburst Galaxies
  Post-starbursts (PSBs) are candidate for rapidly transitioning from
star-bursting to quiescent galaxies. We study the molecular gas evolution of
PSBs at z ~ 0.03 - 0.2. We undertook new CO (2-1) observations of 22 Seyfert
PSBs candidates using the ARO Submillimeter Telescope. This sample complements
previous samples of PSBs by including green valley PSBs with Seyfert-like
emission, allowing us to analyze for the first time the molecular gas
properties of 116 PSBs with a variety of AGN properties. The distribution of
molecular gas to stellar mass fractions in PSBs is significantly different than
normal star-forming galaxies in the COLD GASS survey. The combined samples of
PSBs with Seyfert-like emission line ratios have a gas fraction distribution
which is even more significantly different and is broader (~ 0.03-0.3). Most of
them have lower gas fractions than normal star-forming galaxies. We find a
highly significant correlation between the WISE 12 micron to 4.6 micron flux
ratios and molecular gas fractions in both PSBs and normal galaxies. We detect
molecular gas in 27% of our Seyfert PSBs. Taking into account the upper limits,
the mean and the dispersion of the distribution of the gas fraction in our
Seyfert PSB sample are much smaller (mean = 0.025, std dev. = 0.018) than
previous samples of Seyfert PSBs or PSBs in general (mean ~ 0.1 - 0.2, std dev.
~ 0.1 - 0.2).
