Black hole spin and galactic morphology

We investigate the conjecture by Sikora, Stawarz, and Lasota that the observed active galactic nuclei ( AGNs) radio loudness bimodality can be explained by the morphology-related bimodality of black hole spin distribution in the centers of galaxies: central black holes ( BHs) in giant elliptical galaxies may have ( on average) much larger spins than black holes in spiral/disk galaxies. We study how accretion from a warped disk influences the evolution of black hole spins and conclude that within the cosmological framework, where the most massive BHs have grown in mass via merger-driven accretion, one indeed expects most supermassive black holes in elliptical galaxies to have on average higher spin than black holes in spiral galaxies, where random, small accretion episodes ( e. g., tidally disrupted stars, accretion of molecular clouds) might have played a more important role.