QSO obscuration at high redshift (z ≳ 7): predictions from the BLUETIDES simulation
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- June 2020
- DOI:
- 10.1093/mnras/staa1313
- arXiv:
- arXiv:1912.03780
- Bibcode:
- 2020MNRAS.495.2135N
- Keywords:
-
- galaxies: formation;
- galaxies: high-redshift;
- quasars: supermassive black holes;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- doi:10.1093/mnras/staa1313