Bibcode
Agarwal, Bhaskar; Khochfar, Sadegh; Johnson, Jarrett L.; Neistein, Eyal; Dalla Vecchia, C.; Livio, Mario
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 425, Issue 4, pp. 2854-2871.
Advertised on:
10
2012
Citations
226
Refereed citations
208
Description
We study for the first time the environment of massive black hole (BH)
seeds (˜104-5 M⊙) formed via the direct
collapse of pristine gas clouds in massive haloes (≥107
M⊙) at z > 6. Our model is based on the evolution of
dark matter haloes within a cosmological N-body simulation, combined
with prescriptions for the formation of BH along with both Population
III (Pop III) and Population II (Pop II) stars. We calculate the
spatially varying intensity of Lyman-Werner (LW) radiation from stars
and identify the massive pristine haloes in which it is high enough to
shut down molecular hydrogen cooling. In contrast to previous BH seeding
models with a spatially constant LW background, we find that the
intensity of LW radiation due to local sources, Jlocal, can
be up to ˜106 times the spatially averaged background
in the simulated volume and exceeds the critical value,
Jcrit, for the complete suppression of molecular cooling, in
some cases by four orders of magnitude. Even after accounting for
possible metal pollution in a halo from previous episodes of star
formation, we find a steady rise in the formation rate of direct
collapse BHs (DCBHs) with decreasing redshift from 10-3
Mpc-3 z-1 at z = 12 to 10-2
Mpc-3 z-1 at z = 6. The onset of Pop II star
formation at z ≈ 16 simultaneously marks the onset of the epoch of
DCBH formation, as the increased level of LW radiation from Pop II stars
is able to elevate the local levels of the LW intensity to
Jlocal > Jcrit, while Pop III stars fail to do
so at any time. The number density of DCBHs is sensitive to the number
of LW photons and can vary by over an order of magnitude at z = 7 after
accounting for reionization feedback. Haloes hosting DCBHs are more
clustered than similar massive counterparts that do not host DCBHs,
especially at redshifts z ≳ 10. Also, the DCBHs that form at z >
10 are found to reside in highly clustered regions, whereas the DCBHs
formed around z ˜ 6 are more common. We also show that planned
surveys with James Webb Space Telescope should be able to detect the
supermassive stellar precursors of DCBHs.