Evolution of supermassive black hole spins in the ΛCDM cosmology

Over the last years, several observations suggest that SMBHs likely reside at the centres of all spheroid galaxies. Even more interestingly, their properties seem to correlate with the bulge luminosity – or stellar velocity dispersion – and the bulge mass, suggesting a single mechanism for assembling BHs and forming spheroids in galaxies. We have been investigating the cosmological co-evolution of galaxies and their central SMBH in hierarchical models of galaxy formation, using the semi-analytic model developed in Durham University. We focus on the spin of the SMBHs and study how does it evolve during accretion of gas and mergers with other SMBHs. We conclude that the global SMBH spin distribution in the present universe may be bimodal, provided that the gas is fed into the hole through a self-gravity limited accretion disk.