Nuclear black hole formation in clumpy galaxies at high redshift

Massive stellar clumps in high-redshift galaxies interact and migrate to the center to form a bulge and exponential disk in ≳ 1 Gyr. Here we consider the fate of intermediate-mass black holes (BHs) that might form by massive-star coalescence in the dense young clusters of these disk clumps. We find that the BHs move inward with the clumps and reach the inner few hundred parsecs in only a few orbit times. There they could merge into a supermassive BH by dynamical friction. The ratio of BH mass to stellar mass in the disk clumps is approximately preserved in the final ratio of BH to bulge mass. Because this ratio for individual clusters has been estimated to be ∼10-3, the observed BH-to-bulge mass ratio results. We also obtain a relation between BH mass and bulge velocity dispersion that is compatible with observations of present-day galaxies. © 2008. The American Astronomical Society. All rights reserved.