Well, they have seen arms behind the brightness of some Quasars. If
galaxies that are excited for some reason then channel that energy into
formation of accretion discs which grow into Quasars and are given off,
then we compare that to excited atoms giving off photons. The energy is
not the same as that of the original galaxy, and in fact has different
'spin' than the original galaxy, a fact that is proven by its intrinsic
redshift. So where we see galaxies interacting and subsequently Quasars
being given off, it might be likened to chemical reactions taking place.
John
http://users.accesscomm.ca/john/