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ABSTRACT The James Webb Space Telescope will have the power to characterize high-redshift quasars at z ≥ 6 with an unprecedented depth and spatial resolution. While the brightest quasars at such redshift (i.e. with bolometric luminosity $$L_{\rm bol}\geqslant 10^{46}\, \rm erg/s$$) provide us with key information on the most extreme objects in the Universe, measuring the black hole (BH) mass and Eddington ratios of fainter quasars with $$L_{\rm bol}= 10^{45}-10^{46}\, \rm erg\,s^{ -1}$$ opens a path to understand the build-up of more normal BHs at z ≥ 6. In this paper, we show that the Illustris, TNG100, TNG300, Horizon-AGN, EAGLE, and SIMBA large-scale cosmological simulations do not agree on whether BHs at z ≥ 4 are overmassive or undermassive at fixed galaxy stellar mass with respect to the MBH − M⋆ scaling relation at z = 0 (BH mass offsets). Our conclusions are unchanged when using the local scaling relation produced by each simulation or empirical relations. We find that the BH mass offsets of the simulated faint quasar population at z ≥ 4, unlike those of bright quasars, represent the BH mass offsets of the entire BH population, for all the simulations. Thus, a population of faint quasars with $$L_{\rm bol}= 10^{45}-10^{46}\, \rm erg\,s^{ -1}$$ observed by JWST can provide key constraints on the assembly of BHs at high redshift. Moreover, this will help constraining the high-redshift regime of cosmological simulations, including BH seeding, early growth, and co-evolution with the host galaxies. Our results also motivate the need for simulations of larger cosmological volumes down to z ∼ 6, with the same diversity of subgrid physics, in order to gain statistics on the most extreme objects at high redshift.
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Supermassive black holes in cosmological simulations I: M BH − M ⋆ relation and black hole mass function
ABSTRACT The past decade has seen significant progress in understanding galaxy formation and evolution using large-scale cosmological simulations. While these simulations produce galaxies in overall good agreement with observations, they employ different sub-grid models for galaxies and supermassive black holes (BHs). We investigate the impact of the sub-grid models on the BH mass properties of the Illustris, TNG100, TNG300, Horizon-AGN, EAGLE, and SIMBA simulations, focusing on the MBH − M⋆ relation and the BH mass function. All simulations predict tight MBH − M⋆ relations, and struggle to produce BHs of $$M_{\rm BH}\leqslant 10^{7.5}\, \rm M_{\odot }$$ in galaxies of $$M_{\star }\sim 10^{10.5}\!-\!10^{11.5}\, \rm M_{\odot }$$. While the time evolution of the mean MBH − M⋆ relation is mild ($$\rm \Delta M_{\rm BH}\leqslant 1\, dex$$ for 0 $$\leqslant z \leqslant$$ 5) for all the simulations, its linearity (shape) and normalization varies from simulation to simulation. The strength of SN feedback has a large impact on the linearity and time evolution for $$M_{\star }\leqslant 10^{10.5}\, \rm M_{\odot }$$. We find that the low-mass end is a good discriminant of the simulation models, and highlights the need for new observational constraints. At the high-mass end, strong AGN feedback can suppress the time evolution of the relation normalization. Compared with observations of the local Universe, we find an excess of BHs with $$M_{\rm BH}\geqslant 10^{9}\, \rm M_{\odot }$$ in most of the simulations. The BH mass function is dominated by efficiently accreting BHs ($$\log _{10}\, f_{\rm Edd}\geqslant -2$$) at high redshifts, and transitions progressively from the high-mass to the low-mass end to be governed by inactive BHs. The transition time and the contribution of active BHs are different among the simulations, and can be used to evaluate models against observations.
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- PAR ID:
- 10237288
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 503
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 1940 to 1975
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stab496
