Theoretical Models of Multi-waveband QSO Luminosity Functions
Abstract
Cosmological evolution of the QSO luminosity functions (LFs) at NIR/optical/X-ray bands for 1.3 < z < 3.5 is investigated based on the realistic QSO spectra. The accretion-disk theory predicts that although QSO luminosities only depend on mass-accretion rate, , QSO spectra have a dependence on black-hole mass, MBH, as well. The smaller MBH is and/or the larger is, the harder becomes the QSO NIR/optical/UV spectrum. We model disk spectra which can reproduce these features and calculated LFs for redshift z ~ 3 with the assumption of new-born QSOs being shining at the Eddington luminosity. The main results are: (i) the observed LFs at optical and X-rays can be simultaneously reproduced. (ii) LFs at optical and X-ray bands are not sensitive to MBH, while LFs at NIR bands are; about one order of magnitude difference is expected in volume number densities at LI, J ~ 1046 erg s-1 between the case that all QSOs would have the same spectral shape as that of MBH = 109 Msun and the case with MBH = 1011 Msun. (iii) The resultant LFs at NIR are dominated by 107 Msun black-holes at LI, J ~ 1044 erg s-1, and by 1011 Msun black-holes at LI, J \~ 1046 erg s-1. Future infrared observations from space(e.g.NGST) will probe cosmological evolution of black hole masses. For redshift z < 3, on the other hand, the observed optical/X-ray LFs can be fitted, if the initial QSO luminosity L0 is below the Eddington luminosity. Interestingly, the best fitting values of l = L0/LEdd are different in B- and X-ray bands; lB ~ 2.5 lX. The reason for this discrepancy is briefly discussed.
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