Impact of gas spin and Lyman–Werner flux on black hole seed formation in cosmological simulations: implications for direct collapse. Issue 1 (27th November 2021)

• Record Type: Journal Article
• Authors: Bhowmick, Aklant K; Blecha, Laura; Torrey, Paul; Kelley, Luke Zoltan; Vogelsberger, Mark; Nelson, Dylan; Weinberger, Rainer; Hernquist, Lars
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 510:Issue 1(2022)
• Page Start: 177
• Page End: 196
• Publication Date: 2021-11-27
• Subjects: black hole physics -- galaxies: high-redshift -- galaxies: nuclei; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab3439
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Direct collapse black holes (BHs) are promising candidates for producing massive z ≳ 6 quasars, but their formation requires fine-tuned 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 × M seed and a dense, metal-poor gas mass >5 × M seed . Within this framework, we find that the seed-forming haloes have a prior history of star formation and metal enrichment, but they also contain pockets of dense, metal-poor 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, metal-poor gas is required to have a critical LW flux ( J crit ). Even for J crit values as low as 50 J 21, 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 super-Eddington accretion, or a combination of these possibilities.