Evidence for cosmic evolution in the spin of the most massive black holes

Authors

  • Alejo Martínez-Sansigre,

    Corresponding author
    1. Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX
    2. Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH
    3. SEPnet, South-East Physics network
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  • Steve Rawlings

    1. Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH
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E-mail: alejo.martinez-sansigre@port.ac.uk

ABSTRACT

We use results from simulations of the production of magnetohydrodynamic jets around black holes to derive the cosmic spin history of the most massive black holes. We assume that the efficiency of jet production is a monotonic function of spin inline image, as given by the simulations, and that the accretion flow geometry is similarly thick for quasars accreting close to the Eddington ratio and for low-excitation radio galaxies accreting at very small Eddington rates. We use the ratio of the comoving densities of the jet power to the radiated accretion power associated with supermassive black holes with m≳ 108 M to estimate the cosmic history of the characteristic spin inline image. The evolution of this ratio, which increases with decreasing z, is consistent with a picture where the z∼ 0 active galactic nuclei have typically higher spins than those at z∼ 2 (with typical values inline image–0.95 and ∼0.0–0.25, respectively). We discuss the implications in terms of the relative importance of accretion and mergers in the growth of supermassive black holes with m≳ 108 M.

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