The molecular emission from old supernova remnants
  Supernovae constitute a critical source of energy input to the interstellar
medium (ISM). In this short review, we focus on their latest phase of
evolution, the supernova remnants (SNRs). We present observations of three old
SNRs that have reached the phase where they interact with the ambient ISM: W28,
IC443, and 3C391. We show that such objects make up clean laboratories to
constrain the physical and chemical processes at work in molecular shock
environments. Our studies subsequently allow us to quantify the impact of SNRs
on their environment in terms of mass, momentum, and energy dissipation. In
turn, their contribution to the energy balance of galaxies can be assessed.
Their potential to trigger a further generation of star formation can also be
investigated. Finally, our studies provide strong support for the
interpretation of gamma-ray emission in SNRs, a crucial step to answer
questions related to cosmic rays population and acceleration.
