Properties of High Redshift Quasars-II: What does the quasar luminosity function tell us about super-massive black-hole evolution?

摘要

In the local universe, the masses of Super-Massive Black-Holes (SMBH) appearto correlate with the physical properties of their hosts, including the mass ofthe dark-matter halo. Using these clues as a starting point many studies haveproduced models that can explain phenomena like the quasar luminosity function.The shortcoming of this approach is that working models are not unique, and asa result it is not always clear what input physics is being constrained. Herewe take a different approach. We identify critical parameters that describe theevolution of SMBHs at high redshift, and constrain their parameter space basedon observations of high redshift quasars from the Sloan Digital Sky Survey. Wefind that the luminosity function taken in isolation is somewhat limited in itsability to constrain SMBH evolution due to some strong degeneracies. Thisexplains the presence in the literature of a range of equally successful modelsbased on different physical hypotheses. Including the constraint of the localSMBH to halo mass ratio breaks some of the degeneracies, and our resultssuggest halo masses at z~4.8 of 10^{12.5+/-0.3}M_solar (with 90% confidence),with a SMBH to halo mass ratio that decreases with time (>99%). We also find aquasar luminosity to halo mass ratio that increases with halo mass (>99%).These features need to be incorporated in all successful models of SMBHevolution. On the other hand current observations do not permit any conclusionsregarding the evolution of quasar lifetime, or the SMBH occupation fraction indark matter halos.