南方基地知识库

We build a simple physical model to study the high-redshift active galactic nucleus (AGN) evolution within the coevolution framework of central black holes (BHs) and their host galaxies. The correlation between the circular velocity of a dark halo V-c and the velocity dispersion of a galaxy sigma is used to link the dark matter halo mass and BH mass. The dark matter halo mass function is converted to the BH mass function for any given redshift. The high-redshift optical AGN luminosity functions (LFs) are constructed. At z similar to 4, the flattening feature is not shown at the faint end of the optical AGN LF. This is consistent with observational results. If the optical AGN LF at z similar to 6 can be reproduced in the case in which central BHs have the Eddington-limited accretion, it is possible for the AGN lifetime to have a small value of 2 x 10(5) years. The X-ray AGN LFs and X-ray AGN number counts are also calculated at 2.0 < z < 5.0 and z > 3, respectively, using the same parameters adopted in the calculation for the optical AGN LF at z similar to 4. It is estimated that about 30 AGNs per deg(2) at z > 6 can be detected with a flux limit of 3 x 10(-17) erg cm(-2) s(-1) in the 0.5-2 keV band. Additionally, the cosmic reionization is also investigated. The ultraviolet photons emitted from the high-redshift AGNs mainly contribute to the cosmic reionization, and the central BHs of the high-redshift AGNs have a mass range of 10(6)-10(8)M(circle dot). We also discuss some uncertainties in both the AGN LFs and AGN number counts originating from the M-BH-sigma relation, Eddington ratio, AGN lifetime, and X-ray attenuation in our model.