SUPERMASSIVE SEEDS FOR SUPERMASSIVE BLACK HOLES

Recent observations of quasars powered by supermassive black holes (SMBHs) out to z greater than or similar to 7 constrain both the initial seed masses and the growth of the most massive black holes (BHs) in the early universe. Here we elucidate the implications of the radiative feedback from early generations of stars and from BH accretion for popular models for the formation and growth of seed BHs. We show that by properly accounting for (1) the limited role of mergers in growing seed BHs as inferred from cosmological simulations of early star formation and radiative feedback, (2) the sub-Eddington accretion rates of BHs expected at the earliest times, and (3) the large radiative efficiencies epsilon of the most massive BHs inferred from observations of active galactic nuclei at high redshift (epsilon greater than or similar to 0.1), we are led to the conclusion that the initial BH seeds may have been as massive as greater than or similar to 10(5) M-circle dot. This presents a strong challenge to the Population III seed model, which calls for seed masses of similar to 100 M-circle dot and, even with constant Eddington-limited accretion, requires epsilon less than or similar to 0.09 to explain the highest-z SMBHs in today's standard.CDM cosmological model. It is, however, consistent with the prediction of the direct collapse scenario of SMBH seed formation, in which a supermassive primordial star forms in a region of the universe with a high molecule-dissociating background radiation field, and collapses directly into a 10(4)-10(6) M-circle dot seed BH. These results corroborate recent cosmological simulations and observational campaigns which suggest that these massive BHs were the seeds of a large fraction of the SMBHs residing in the centers of galaxies today.