Determination of supermassive black hole spins in active galactic nuclei

Abstract

Abstract Black hole spin is a key to the relativistic jet generation. Existing models are based on the Blandford–Znajek and/or Blandford–Payne mechanisms. The jet power in these models is determined by the spin value, black hole mass, magnetic fields at the event horizon, and the accretion disc. Independent estimates of mass, jet power, and magnetic field give opportunity to constrain the supermassive black hole spin value. We present an application of this approach for supermassive black holes in different samples of active galactic nuclei (AGNs). We found that the assumption about equipartition between magnetic field energy density and accreting matter energy density is reasonable for the systems with thin accretion discs. The “mass-spin” diagrams were constructed for the samples of PG quasars and distant quasars at redshift z ≈ 4.8 and demonstrated the flattening region at masses MBH ≈ 108.5M☉. These diagrams can be used to study accretion onto supermassive black holes.