Recent deep surveys have unravelled a population of faint active galactic nuclei ( AGN ) in the high redshift Universe , leading to various discussions on their nature and their role during the Epoch of Reionization .
We use cosmological radiation-hydrodynamics simulations of a bright galaxy at z \sim 6 ( { M _ { \star } } \gtrsim \SI { e 10 } { \Msun } ) hosting an actively growing super-massive black hole to study the properties of these objects .
In particular , we study how the black hole and the galaxy co-evolve and what is the relative contribution of the AGN and of the stellar populations to the luminosity budget of the system .
We find that the feedback from the AGN has no strong effect on the properties of the galaxy , and does not increase the total ionizing luminosity of the host .
The average escape fraction of our galaxy is around f _ { esc } \sim 5 \% .
While our galaxy would be selected as an AGN in deep X-ray surveys , most of the UV luminosity is originating from stellar populations .
This confirms that there is a transition in the galaxy population from star forming galaxies to quasar hosts , with bright Lyman-Break Galaxies ( LBGs ) with { M } _ { UV } around -22 falling in the overlap region .
Our results also suggest that faint AGN do not contribute significantly to reionizing the Universe .