Supernova remnants colliding with molecular clouds: From high- to low-energy interactions

It is now well established that a class of gamma-ray sources in the galactic plane, especially in the TeV range as seen by HESS and other Cerenkov telescopes, and in the GeV range by the Fermi and AGILE satellites, is associated with intermediate-age supernova remnants interacting with molecular clouds in massive star-forming regions. After a brief general introduction linking high-energy gamma-rays and cosmic rays, I will focus on a few such gamma-ray sources (W28, W44, and W51) and the challenging conclusions that can be drawn from them. I will then describe our recent work on related submm measurements and implications of enhanced ionizing effects in molecular clouds due to locally accelerated low-energy cosmic rays.