QSO obscuration at high redshift (z ≳ 7): predictions from the BLUETIDES simulation

Journal
Date Issued
2020
Author(s)
Ni, Yueying
•
Di Matteo, Tiziana
•
•
Croft, Rupert A. C.
•
Feng, Yu
•
Norman, Colin
DOI
Abstract
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 NH. The brightest quasars can have large angular variations in galactic obscuration, over 2 orders of magnitude (ranging from column density NH ∼ 1021.5-24 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(NH > 1023 cm-2) typically ranges from 0.6 to 1.0 for increasing LX (with LX > 1043 erg cm-1), with no clear trend of redshift evolution. Due to the angular variation in NH, all relations between NH and LX, MBH, and galaxy host properties (global M*, MH2, and star formation rate) show appreciable scatter. The dust optical depth in the UV band τUV has tight positive correlation with NH. 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.
Volume
495
Issue
2
Start page
2135
Uri
Url
Issn Identifier
0035-8711
Ads BibCode
2020MNRAS.495.2135N
Rights
open.access
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