Cosmological Evolution Models for QSO/Active Galactic Nucleus Luminosity Functions: Effects of Spectrum‐Luminosity Correlation and Massive Black Hole Remnants

We investigate a large number of cosmological evolution models for QSOs andActive Galactic Nuclei (AGN). We introduce a spectrum-luminosity correlation asa new input parameter and adopt the estimated mass function (MF) of massiveblack holes in centers of nearby galactic nuclei as a constraint to distinguishamong different QSO/AGN models. We explore three basic types ofphenomenological scenarios; (i) Models with multiple short-lived ($\sim$ a few$10^{6-8}$ yrs) populations, (ii) Models with a single long-lived ($\sim 10^9$yr) QSO population, and (iii) Models with recurrent QSO/AGN activities whichare driven by long-term variabilities of the disk instability type. In eachmodel, we derive the expected theoretical luminosity function (LF) and the MFof black holes which grow through mass accretion. We assess the plausibility ofeach model based on whether each model's LF and MF are compatible with theobserved data. We find that the best fits to the observed LFs are obtained inthe model with multiple short-lived populations and without any significantspectral evolution. This finding suggests that the QSO populations may becomposed of many short-lived generations ($\sim$ a few 10$^8$ yrs) and thatthere is no significant spectral evolution within each generation. On the otherhand, we also show that there is no satisfactory model which can simultaneouslyaccount for the observed LF and the estimated MF. We speculate that some of thepresent-day black holes (BHs) found in galactic nuclei may have formed withoutundergoing the QSO/AGN phase.Comment: 21 pages, 6 figures, submitted to Ap