But then we expect to see massive luminous objects in all Galaxies. Recent surveys indicate there are massive objects but they do not give off light. Evidence is consistent with Black Holes. Are you aware of the work done on analying the spectra of Quasars. Big Stars like S. Doradus have distinct spectra.
Galactic spectra are different as they contain the light from millions of stars.
Did you know that Quasars are associated with BL Lacertae objects, Seyfert Galaxies and other Active Galactic Nuclei. All the evidence points to Quasars as Black Holes with jets and large clouds of highly ionised gas clouds orbiting the Hole. See previous evidence on Hubble Deep Field. These then orbit the central bulge of our galaxies to make up its structure that one can quite clearly see that such matter ejections has the ability to create the spiral arms of a barred galaxy or spiral galaxy or elliptical galaxy . But how do you explain the variations in these galactic morphologies.