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Supermassive black holes in cosmological simulations I: MBH − M⋆ relation and black hole mass function

Habouzit, Mélanie and Li, Yuan and Somerville, Rachel S and Genel, Shy and Pillepich, Annalisa and Volonteri, Marta and Davé, Romeel and Rosas-Guevara, Yetli and McAlpine, Stuart and Peirani, Sébastien and Hernquist, Lars and Anglés-Alcázar, Daniel and Reines, Amy and Bower, Richard and Dubois, Yohan and Nelson, Dylan and Pichon, Christophe and Vogelsberger, Mark (2021) 'Supermassive black holes in cosmological simulations I: MBH − M⋆ relation and black hole mass function.', Monthly notices of the Royal Astronomical Society, 503 (2). pp. 1940-1975.


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 MBH⩽107.5M⊙ in galaxies of M⋆∼1010.5−1011.5M⊙⁠. While the time evolution of the mean MBH − M⋆ relation is mild (⁠ΔMBH⩽1dex for 0 ⩽z⩽ 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⋆⩽1010.5M⊙⁠. 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 MBH⩾109M⊙ in most of the simulations. The BH mass function is dominated by efficiently accreting BHs (⁠log10fEdd⩾−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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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:16 February 2021
Date deposited:15 July 2021
Date of first online publication:22 February 2021
Date first made open access:15 July 2021

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