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arXiv · 1609.03753

On the Evolution of High-Redshift Active Galactic Nuclei

Jirong Mao·Minsun Kim
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Abstract

We build a simple physical model to study the high-redshift active galactic Nucleus (AGN) evolution within the co-evolution 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 $z\sim 4$, 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 $z\sim 6$ 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 $2\times 10^5$ yrs. The X-ray AGN LFs and X-ray AGN number counts are also calculated at $2.0 3$, respectively, using the same parameters adopted in the calculation for the optical AGN LF at $z\sim 4$. It is estimated that about 30 AGNs per $\rm{deg}^2$ at $z>6$ can be detected with a flux limit of $3\times 10^{-17}~\rm{erg~cm^{-2}~s^{-1}}$ 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 $10^6-10^8M_\odot$. We also discuss some uncertainties in both the AGN LFs and AGN number counts originating from the $M_{\rm{BH}}-\sigma$ relation, Eddington ratio, AGN lifetime, and X-ray attenuation in our model.

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Jirong Mao, Minsun Kim. 2016-09-13. On the Evolution of High-Redshift Active Galactic Nuclei. https://doi.org/10.3847/0004-637x/828/2/96

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