The aftermath of the first stars: massive black holes

We investigate the evolution of the primordial gas surrounding the first massive black holes formed by the collapse of Population III stars at redshifts z greater than or similar to 20. Carrying out three-dimensional hydrodynamical simulations using GADGET, we study the dynamical, thermal and chemical evolution of the first relic H II regions. We also carry out simulations of the mergers of relic H II regions with neighbouring neutral minihaloes, which contain high-density primordial gas that could accrete on to a Population III remnant black hole. We find that there may have been a significant time delay, of the order of similar to 10(8) yr, between black hole formation and the onset of efficient accretion. The build-up of supermassive black holes, believed to power the z greater than or similar to 6 quasars observed in the Sloan Digital Sky Survey, therefore faces a crucial early bottleneck. More massive seed black holes may thus be required, such as those formed by the direct collapse of a primordial gas cloud facilitated by atomic line cooling. The high optical depth to Lyman-Werner (LW) photons that results from the high fraction of H-2 molecules that form in relic H II regions, combined with the continued formation of H-2 inside the dynamically expanding relic H II region, leads to shielding of the molecules inside these regions at least until a critical background LW flux of similar to 10(-24) erg s(-1) cm(-2) Hz(-1) sr(-1) is established. Furthermore, we find that a high fraction of deuterium hydride (HD) molecules, >X-HD greater than or similar to 10(-7), is formed, potentially enabling the formation of Population II.5 stars, with masses of the order of similar to 10 M-circle dot, during later stages of structure formation when the relic H II region gas is assembled into a sufficiently deep potential well to gravitationally confine the gas again.