  Usual supernova remnants have either ionizing plasma or plasma in collisional
ionization equilibrium, i.e., the ionization temperature is lower than or equal
to the electron temperature. However, the existence of recombining supernova
remnants, i.e., supernova remnants with the ionization temperature higher than
the electron temperature, is recently confirmed. One suggested way to have
recombining plasma in a supernova remnant is to have a dense circumstellar
medium at the time of the supernova explosion. If the circumstellar medium is
dense enough, collisional ionization equilibrium can be established in the
early stage of the evolution of the supernova remnant and subsequent adiabatic
cooling which occurs after the shock wave gets out of the dense circumstellar
medium makes the electron temperature lower than the ionization temperature. We
study the circumstellar medium around several supernova progenitors and show
which supernova progenitors can have a circumstellar medium which is dense
enough to establish collisional ionization equilibrium soon after the
explosion. We find that the circumstellar medium around red supergiants
(especially massive ones) and the circumstellar medium which is dense enough to
make Type IIn supernovae can establish collisional ionization equilibrium soon
after the explosion and can evolve to recombining supernova remnants.
Wolf-Rayet stars and white dwarfs have possibility to be recombining supernova
remnants but the fraction is expected to be very small. As the occurrence rate
of the explosions of red supergiants is much higher than that of Type IIn
supernovae, the major progenitors of recombining supernova remnants are likely
to be red supergiants.
