On the formation of disk galaxies and massive central objects

We propose that massive central objects form in the centers of the bars tha t must develop in young high surface density galactic disks. Large-scale dy namics shut off the growth of the central mass before it reaches similar to 2% of the disk mass at the time, but this mass is sufficient to substantia lly weaken the bar. Subsequent evolution of the galaxy can either complete the destruction of the bar or cause it to recover, depending on the angular momentum distribution of later infalling material. We produce massive, ful ly self-gravitating disks having roughly hat rotation curves that are quite stable. If at least part of the central masses we require constitute the e ngines of QSOs, then our picture naturally accounts for their redshift depe ndence since the fuel supply is shut off by the development of an inner Lin dblad resonance. A prediction is that massive objects should not be found i n halo-dominated galaxies such as low-luminosity or low surface brightness galaxies.