Heating of the Warm Ionized Medium by Low-Energy Cosmic Rays
  In light of evidence for a high ionization rate due to Low-Energy Cosmic Rays
(LECR), in diffuse molecular gas in the solar neighbourhood, we evaluate their
heat input to the Warm Ionized Medium (WIM). LECR are much more effective at
heating plasma than they are at heating neutrals. We show that the upper end of
the measured ionization rates corresponds to a local LECR heating rate
sufficient to maintain the WIM against radiative cooling, independent of the
nature of the ionizing particles or the detailed shape of their spectrum.
Elsewhere in the Galaxy the LECR heating rates may be higher than measured
locally. In particular, higher fluxes of LECR have been suggested for the inner
Galactic disk, based on the observed hard X-ray emission, with correspondingly
larger heating rates implied for the WIM. We conclude that LECR play an
important, perhaps dominant role in the thermal balance of the WIM.
