Star formation and black hole accretion at high redshift (review)

Various ways to probe the co-evolution of super massive black holes and their host galaxies are reviewed and discussed. An integrated approach to the problem, involving the measurement of black holes (BHs) and galaxy masses at all redshifts, is compared with a differential instantaneous way where the observables are the active galactic nucleus (AGN) luminosity, LAGN, and the star formation luminosity, LSF. The missing ingredients in both methods are the mass function and duty cycle of BHs. I demonstrate how new data on very high redshift objects enable first reliable estimates of the duty cycles of the most massive BHs, and argue that the extreme star formation rates in their host galaxies indicate large mergers. The idea of creating a "BH mass sequence" is examined using data from large AGN surveys. While this is a promising method, most present day data are inadequate for such an analysis because of various selection effects. I present a new attempt to use semi-analytic models to explain new observations of LAGN versus LSF in various samples observed by Herschel. The model indicates that a scenario where BH accretion is triggered by mergers is in good agreement with observations despite various suggestions that secular evolution plays a more important role in most AGNs.