Radiation Hydrodynamical Simulations of the Birth of Intermediate-Mass Black Holes in the First Galaxies
Abstract
The leading contenders for the seeds of z > 6 quasars are direct-collapse black holes (DCBHs) forming in atomically-cooled halos at z 20. However, the Lyman-Werner (LW) UV background required to form DCBHs of 105 \ are extreme, about 104 J21, and may have been rare in the early universe. Here we investigate the formation of intermediate-mass black holes (IMBHs) under moderate LW backgrounds of 100 and 500 J21 that were much more common at early times. These backgrounds allow halos to grow to a few 106 - 107 \ and virial temperatures of nearly 104 K before collapsing but do not completely sterilize them of H2. Gas collapse then proceeds via Lyα and rapid H2 cooling at rates that are 10 - 50 times those in normal Pop III star-forming haloes but less than those in purely atomically-cooled haloes. Pop III stars accreting at such rates become blue and hot, and we find that their ionizing UV radiation limits their final masses to 1800 - 2800 \, at which they later collapse to IMBHs. Moderate LW backgrounds thus produced IMBHs in far greater numbers than DCBHs in the early universe.