Ubiquitous seeding of supermassive black holes by direct collapse

Abstract

We study for the first time the environment of massive black hole (BH) seeds\n(~10^4-5 Msun) formed via the direct collapse of pristine gas clouds in massive\nhaloes (>10^7 Msun) at z>6. Our model is based on the evolution of dark matter\nhaloes within a cosmological N-body simulation, combined with prescriptions for\nthe formation of BH along with both Pop III and Pop II stars. We calculate the\nspatially-varying intensity of Lyman Werner (LW) radiation from stars and\nidentify the massive pristine haloes in which it is high enough to shut down\nmolecular hydrogen cooling. In contrast to previous BH seeding models with a\nspatially constant LW background, we find that the intensity of LW radiation\ndue to local sources, J_local, can be up to 10^6 times the spatially averaged\nbackground in the simulated volume and exceeds the critical value, J_crit, for\nthe complete suppression of molecular cooling, in some cases by 4 orders of\nmagnitude. Even after accounting for possible metal pollution in a halo from\nprevious episodes of star formation, we find a steady rise in the formation\nrate of direct collapse (DC) BHs with decreasing redshift from 10^{-3}/Mpc^3/z\nat z=12 to 10^{-2}/Mpc^3/z at z=6. The onset of Pop II star formation at z~16\nsimultaneously marks the onset of the epoch of DCBH formation, as the increased\nlevel of LW radiation from Pop II stars is able to elevate the local levels of\nthe LW intensity to J_local > J_crit while Pop III stars fail to do so at any\ntime. The number density of DCBHs is sensitive to the number of LW photons and\ncan vary by an order of magnitude at z=6 after accounting for reionisation\nfeedback. Haloes hosting DCBHs are more clustered than similar massive\ncounterparts that do not host DCBHs, especially at redshifts z>10. We also show\nthat planned surveys with JWST should be able to detect the supermassive\nstellar precursors of DCBHs.\n