2020MNRAS.495.2135N

High-z AGNs hosted in gas-rich galaxies are expected to grow through significantly obscured accretion phases. This may limit or bias their observability. In this work, we use BLUETIDES, a large volume cosmological simulation of galaxy formation to examine quasar obscuration for the highest redshift (z >= 7) supermassive black holes residing in the centre of galaxies. We find that for the bright quasars, most of the high-column density gas ( > 90 per cent) resides in the innermost regions of the host galaxy (typically within <10 ckpc), while the gas in the outskirts is a minor contributor to the N_H. The brightest quasars can have large angular variations in galactic obscuration, over 2 orders of magnitude (ranging from column density N_H ∼10^21.5 - 24^ cm^–2), where the lines of sight with the lowest obscuration are those formed via strong gas outflows driven by AGN feedback. The obscured fraction P(N_H > 10²³ cm^–2) typically ranges from 0.6 to 1.0 for increasing L_X (with L_ X_ > 10⁴³ erg s^–1), with no clear trend of redshift evolution. Due to the angular variation in N_H, all relations between N_H and L_X, M_BH, and galaxy host properties (global M_*, M_H2, and star formation rate) show appreciable scatter. The dust optical depth in the UV band τ_UV has tight positive correlation with N_H. Our dust-extincted UV luminosity function (UVLF) is about 1.5 dex lower than the intrinsic UVLF, implying that more than 99 per cent of the z ∼ 7 AGNs are heavily dust extincted and therefore would be missed by the UV-band observation.