研究成果・発表論文

Theoretical Models of Multi-Waveband QSO Luminosity Functions

Hosokawa, Takashi,   Mineshige, Shin,   Kawaguchi, Toshihiro,   Yoshikawa, Kohji,   & Umemura, Masayuki


要旨
The cosmological evolution of the QSO luminosity functions (LFs) at NIR/optical/X-ray bands for 1.3 <åisebox-0.5ex~ z <\i̊sebox-0.5ex~ 3.5 is discussed based on realistic QSO spectra. The accretion-disk theory predicts that although the QSO luminosities only depend on the mass-accretion rate, dot\M\, the QSO spectra have dependence on the black- hole mass, M$_BH$, as well. The smaller is M$_BH$ and/or the larger is dot\M\, the harder does the QSO NIR/optical/UV spectrum become. We modeled the disk spectra which can reproduce these features, and calculated the LFs for a redshift of z \rs̊ebox-0.5ex~ 3 with the assumption of new- born QSOs shining at the Eddington luminosity. The main results are: (i) the LFs observed at optical and X-ray bands can be simultaneously reproduced. (ii) LFs in the optical and X-ray bands are not sensitive to M$_BH$, while LFs at the NIR bands are; about a one order of magnitude difference is expected in the volume number densities at L$_I,J$ \rae̊box-0.5ex~ 10$^46$ erg s$^-1$ between the case that all QSOs would have the same spectral shape as that of M$_BH$ = 10$^9$Msolar and the case with M$_BH$ = 10$^11$ Msolar. (iii) The resultant LFs at NIR are dominated by black holes at L$_I,J$ <\raib̊ox-0.5ex~ 10$^44$ erg s$^-1$, and by 10$^11$Msolar black holes at L$_I,J$ >\raiso̊x-0.5ex~ 10$^46$ erg s$^-1$. Future infrared observations from space (e.g. NGST) will probe the cosmological evolution of black-hole masses. For a redshift of z < 3, on the other hand, the observed optical/X-ray LFs can be fitted if the initial QSO luminosity, L$_0$, is below the Eddington luminosity, L$_Edd$. Interestingly, the best- fitted values of l \ensuremath≡ L$_0$/L$_Edd$ are different in the B- and X-ray bands; l$_B$ \ensuremath≈ 2.5 l$_x$. The reason for this discrepancy is briefly discussed.




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