Yohan Dubois, Marta Volonteri, Joseph Silk
Supermassive black holes (BH) at the centres of galaxies can rapidly change their mass and spin by gas accretion and mergers. Using hydrodynamical cosmological simulations, with prescriptions for BH growth and feedback from Active Galactic Nuclei, we study the evolution of BH spins and we highlight the mechanisms responsible for driving the amplitude and the direction of spins as a function of cosmic time. We find that in the high-redshift universe, galaxies maintain large values of gas accretion onto BHs. BHs tend to align their spins with the angular momentum of the surrounding gas and maximise their amplitude. On the opposite, at low redshift, as BHs get more massive, the contribution from binary coalescence to the total BH mass growth increases and tends to decrease the amplitude of spins and change their direction.
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http://arxiv.org/abs/1304.4583
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