compared to early type galaxies. If morphological quenching is already lowering the dense gas fraction in early type galaxies compared to star forming and starbursting galaxies, this would explain why we do not see a significant difference in the dense gas fractions of the post-starburst and early-type galaxies.

Another possible energy source is the dissipation of turbulence from AGN jets or shocks [@Nesvadba2010]. However, the role of turbulent energy is complex, even in “normal” star-forming galaxies, simultaneously increasing the dense gas fraction by driving collapse at small scales, and suppressing star formation by preventing the collapse of GMCs on larger scales [e.g., @Federrath2013]. @Guillard2015 suggest that heating from the dissipation of AGN-injected turbulence inhibits gravitational collapse on all scales as it cascades.

Conversely, turbulence from stellar feedback is invoked to explain the high gas densities and high dense gas fractions in ULIRGs [e.g., @Papadopoulos2012; @Hopkins2013]. More detailed modeling of the gas state in this unusual suppressed state is needed to understand how various sources of kinetic energy can act to lower the dense gas fraction in these galaxies.

What then is the physical source of the injected energy? Many dynamical times have passed since the starburst ended, so energy or 