科研之友
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摘要
We study the birth of supermassive black holes from the direct collapse process and characterize the sites where these black hole seeds form. In the pre-reionization epoch, molecular hydrogen (H-2) is an efficient coolant, causing gas to fragment and form Population III stars, but Lyman-Werner radiation can suppress H-2 formation and allow gas to collapse directly into a massive black hole. The critical flux required to inhibit H-2 formation, J(crit), is hotly debated, largely due to the uncertainties in the source radiation spectrum, H-2 self-shielding, and collisional dissociation rates. Here, we test the power of the direct collapse model in a self-consistent, time-dependant, nonuniform Lyman-Werner radiation field-the first time such has been done in a cosmological volume-using an updated version of the Smooth Particle Hydrodynamics (SPH)+ N-body tree code GASOLINE with H-2 nonequilibrium abundance tracking, H-2 cooling, and a modern SPH implementation. We vary J(crit) from 30 to 10(3) in units of J(21) to study how this parameter impacts the number of seed black holes and the type of galaxies that host them. We focus on black hole formation as a function of environment, halo mass, metallicity, and proximity of the Lyman-Werner source. Massive black hole seeds form more abundantly with lower J(crit) thresholds, but regardless of J(crit), these seeds typically form in halos that have recently begun star formation. Our results do not confirm the proposed atomic cooling halo pair scenario; rather, black hole seeds predominantly form in low-metallicity pockets of halos that already host star formation.
- 出版日期2018-7-1
