Ray Tomes wrote:

Although the fog mainly scatters the light it cannot absorb it without
re-radiating at some other frequency. What I would like to know is the
equivalent thing for low frequency e/m waves between the galaxies? There
must be a resulting distribution of frequencies that the low frequencies
get converted to surely?

If EM radiation is below the plasma frequency, it doesn't propagate
at all, but is reflected. If the transmitter is embedded in a plasma
it doesn't radiate, or (if strong enough) blows a bubble in the plasma
due to radiation pressure. Some of the energy also gets dissipated
as heat due to the plasma's nonzero resistivity.

Paul