Observational links between AGN evolution and galaxy growth
  There is growing interest in the possible link between the growth of supermassive black holes and the effect of feedback from them on galaxy growth. There are three areas of significant uncertainty: (i) the physics of the feedback; (ii) the prevalence and effectiveness of feedback; (iii) the link between the growth of black holes and their hosts. The 2QZ optical QSO survey indicates that luminous QSOs are relatively short-lived, and it has recently been shown that the observed bolometric luminosity density from all AGN and its evolution can be reproduced if black holes grew coevally with their galaxies, implying but not requiring a causal link between galaxy growth and black hole growth. At low redshifts there is some evidence that black hole and galaxy growth are starting to decouple. 
L. Miller