Direct collapse black holes (BHs) are promising candidates for producing massive z ≳ 6 quasars, but their formation requires finetuned conditions. In this work, we use cosmological zoom simulations to study systematically the impact of requiring: (1) low gas angular momentum (spin), and (2) a minimum incident Lyman–Werner (LW) flux in order to form BH seeds. We probe the formation of seeds (with initial masses of $M_{\rm seed} \sim 10^4\!\!10^6\, \mathrm{M}_{\odot }\, h^{1})$ in haloes with a total mass >3000 × Mseed and a dense, metalpoor gas mass >5 × Mseed. Within this framework, we find that the seedforming haloes have a prior history of star formation and metal enrichment, but they also contain pockets of dense, metalpoor gas. When seeding is further restricted to haloes with low gas spins, the number of seeds formed is suppressed by factors of ∼6 compared to the baseline model, regardless of the seed mass. Seed formation is much more strongly impacted if the dense, metalpoor gas is required to have a critical LW flux (Jcrit). Even for Jcrit values as low as 50J21, no $8\times 10^{5}~\mathrm{M}_{\odot }\, h^{1}$ seeds are formed. While lower mass ($1.25\times 10^{4},1\times 10^{5}~\mathrm{M}_{\odot }\, h^{1}$) seeds do form, they are strongly suppressed (by factors of ∼10–100) compared to the baseline model at gas mass resolutions of $\sim 10^4~\mathrm{M}_{\odot }\, h^{1}$ (with even stronger suppression at higher resolutions). As a result, BH merger rates are also similarly suppressed. Since early BH growth is dominated by mergers in our models, none of the seeds are able to grow to the supermassive regime ($\gtrsim 10^6~\mathrm{M}_{\odot }\, h^{1}$) by z = 7. Our results hint that producing the bulk of the z ≳ 6 supermassive BH population may require alternate seeding scenarios that do not depend on the LW flux, early BH growth dominated by rapid or superEddington accretion, or a combination of these possibilities.
Formation of supermassive black holes (BHs) remains a theoretical challenge. In many models, especially beginning from stellar relic ‘seeds,’ this requires sustained superEddington accretion. While studies have shown BHs can violate the Eddington limit on accretion disc scales given sufficient ‘fuelling’ from larger scales, what remains unclear is whether or not BHs can actually capture sufficient gas from their surrounding interstellar medium (ISM). We explore this in a suite of multiphysics highresolution simulations of BH growth in magnetized, starforming dense gas complexes including dynamical stellar feedback from radiation, stellar massloss, and supernovae, exploring populations of seeds with masses $\sim 1\!\!10^{4}\, \mathrm{M}_{\odot }$. In this initial study, we neglect feedback from the BHs: so this sets a strong upper limit to the accretion rates seeds can sustain. We show that stellar feedback plays a key role. Complexes with gravitational pressure/surface density below $\sim 10^{3}\, \mathrm{M}_{\odot }\, {\rm pc^{2}}$ are disrupted with low star formation efficiencies so provide poor environments for BH growth. But in denser cloud complexes, early stellar feedback does not rapidly destroy the clouds but does generate strong shocks and dense clumps, allowing $\sim 1{{\ \rm per\ cent}}$ of randomly initialized seeds to encounter a dense clump with low relative velocity and produce runaway, hyperEddington accretion (growing by orders of magnitude). Remarkably, mass growth under these conditions is almost independent of initial BH mass, allowing rapid intermediatemass black hole (IMBH) formation even for stellarmass seeds. This defines a necessary (but perhaps not sufficient) set of criteria for runaway BH growth: we provide analytic estimates for the probability of runaway growth under different ISM conditions.
more » « less NSFPAR ID:
 10383259
 Publisher / Repository:
 Oxford University Press
 Date Published:
 Journal Name:
 Monthly Notices of the Royal Astronomical Society
 Volume:
 518
 Issue:
 3
 ISSN:
 00358711
 Format(s):
 Medium: X Size: p. 36063621
 Size(s):
 p. 36063621
 Sponsoring Org:
 National Science Foundation
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