# Molecular Gas during the Post-Starburst Phase: Low Gas Fractions in Green Valley Seyfert Post-Starburst Galaxies

## TL;DR

This study investigates molecular gas content in post-starburst galaxies, especially those with Seyfert activity, revealing generally low gas fractions and correlations with infrared flux ratios, indicating rapid gas depletion during galaxy transition.

## Contribution

It provides the first comprehensive analysis of molecular gas properties in a large, diverse sample of PSBs, including green valley Seyfert PSBs, highlighting their low gas fractions and relation to AGN activity.

## Key findings

- Most PSBs have lower gas fractions than normal star-forming galaxies.
- A significant correlation exists between infrared flux ratios and molecular gas fractions.
- Seyfert PSBs show even smaller gas fractions compared to previous samples.

## Abstract

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).