Massive black holes as population III remnants

Recent numerical simulations of the fragmentation of primordial molecular c louds in hierarchical cosmogonies have suggested that the very first stars (the so-called Population III) may have been rather massive. Here we point out that a numerous population of massive black holes (MBHs)-with masses in termediate between those of stellar and supermassive holes-may be the end p roduct of such an episode of pregalactic star formation. If only one MBH wi th m(.) greater than or similar to 150 M. formed in each of the "minihalos" collapsing at z approximate to 20 from 3 sigma fluctuations, then the mass density of Population III MBHs would be comparable to that of the supermas sive variety observed in the nuclei of galaxies. Since they form in high-si gma rare density peaks, relic MBHs are predicted to cluster in the bulges o f present-day galaxies as they become incorporated through a series of merg ers into larger and larger systems. Dynamical friction would cause greater than or similar to 50 (m(.) /150 M.)(1/2) such objects to sink toward the c enter. The presence of a small cluster of MBHs in galaxy nuclei may have se veral interesting consequences associated with it, such as tidal captures o f ordinary stars (likely followed by disruption), MBH capture by the centra l supermassive black hole, and gravitational wave radiation from such coale scences. Accreting pregalactic MBHs may be detectable as ultraluminous, off -nuclear X-ray sources.