After The Fall: The Dust and Gas in E+A Post-Starburst Galaxies
  The traditional picture of post-starburst galaxies as dust- and gas-poor
merger remnants, rapidly transitioning to quiescence, has been recently
challenged. Unexpected detections of a significant ISM in many post-starbursts
raise important questions. Are they truly quiescent and, if so, what mechanisms
inhibit further star formation? What processes dominate their ISM energetics?
We present an infrared spectroscopic and photometric survey of 33 SDSS-selected
E+A post-starbursts, aimed at resolving these questions. We find compact, warm
dust reservoirs with high PAH abundances, and total gas and dust masses
significantly higher than expected from stellar recycling alone. Both PAH/TIR
and dust-to-burst stellar mass ratios are seen to decrease with post-burst age,
indicative of the accumulating effects of dust destruction and an incipient
transition to hot, early-type ISM properties. Their infrared spectral
properties are unique, with dominant PAH emission, very weak nebular lines,
unusually strong H$_{2}$ rotational emission, and deep ${\rm [C\, II]}$
deficits. There is substantial scatter among SFR indicators, and both PAH and
TIR luminosities provide overestimates. Even as potential upper limits, all
tracers show that the SFR has typically experienced a more than two
order-of-magnitude decline since the starburst, and that the SFR is
considerably lower than expected given both their stellar masses and molecular
gas densities. These results paint a coherent picture of systems in which star
formation was, indeed, rapidly truncated, but in which the ISM was
$\textit{not}$ completely expelled, and is instead supported against collapse
by latent or continued injection of turbulent or mechanical heating. The
resulting aging burst populations provide a "high-soft" radiation field which
seemingly dominates the E+As' unusual ISM energetics.
