Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 490, Issue 3, Pages 4134-4154Publisher
OXFORD UNIV PRESS
DOI: 10.1093/mnras/stz2836
Keywords
accretion, accretion discs; Black hole physics; methods: numerical; quasars: supermassive black holes
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Funding
- International Max-Planck Research School for Astronomy and Cosmic Physics of Heidelberg (IMPRS-HD)
- Deutscher Akademischer Austauschdienst (DAAD) through the Research Grants - Doctoral Programmes in Germany [57129429]
- European Research Council [EXAGAL308037]
- 'The Milky Way System' of the German Science Foundation [SFB-881]
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It is well established that the properties of supermassive black holes (BHs) and their host galaxies are correlated through scaling relations. While hydrodynamical cosmological simulations have begun to account for the coevolution of BHs and galaxies, they typically have neglected the BH spin, even though it may play an important role in modulating the growth and feedback of BHs. Here we introduce a new sub-grid model for the BH spin evolution in the moving-mesh code AREPO in order to improve the physical faithfulness of the BH modelling in galaxy formation simulations. We account for several different channels of spin evolution, in particular gas accretion through a Shakura-Sunyaev alpha-disc, chaotic accretion, and BH mergers. For BH feedback, we extend the IllustrisTNG model, which considers two different BH feedback modes, a thermal quasar mode for high accretion states and a kinetic mode for low Eddington ratios, with a self-consistent accounting of spin-dependent radiative efficiencies and thus feedback strength. We find that BHs with a mass M-bh less than or similar to 10(8) M-circle dot reach high spin values as they typically evolve in the coherent gas accretion regime, in which consecutive accretion episodes are aligned. On the other hand, BHs with a mass M-bh greater than or similar to 10(8) M-circle dot have lower spins as BH mergers become more frequent, and their accretion discs fragment due to self-gravity, inducing chaotic accretion. We also explore the hypothesis that the transition between the quasar and kinetic feedback modes is mediated by the accretion mode of the BH disc itself, i.e. the kinetic feedback mode is activated when the disc enters the self-gravity regime instead of by an ad hoc switch tied to the BH mass. We find excellent agreement between the galaxy and BH populations for this approach and the fiducial TNG model with no spin evolution. Furthermore, our new approach alleviates a tension in the galaxy morphology-colour relation of the original TNG model.
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