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ABSTRACT We explore implications of a range of black hole (BH) seeding prescriptions on the formation of the brightest $$z$$ ≳ 6 quasars in cosmological hydrodynamic simulations. The underlying galaxy formation model is the same as in the IllustrisTNG simulations. Using constrained initial conditions, we study the growth of BHs in rare overdense regions (forming $$\gtrsim 10^{12}\, {\rm M}_{\odot }\,h^{-1}$$ haloes by $$z$$ = 7) using a (9 Mpc h−1)3 simulated volume. BH growth is maximal within haloes that are compact and have a low tidal field. For these haloes, we consider an array of gas-based seeding prescriptions wherein $$M_{\mathrm{seed}}=10^4\!-\!10^6\, {\rm M}_{\odot }\,h^{-1}$$ seeds are inserted in haloes above critical thresholds for halo mass and dense, metal-poor gas mass (defined as $$\tilde{M}_{\mathrm{h}}$$ and $$\tilde{M}_{\mathrm{sf,mp}}$$, respectively, in units of Mseed). We find that a seed model with $$\tilde{M}_{\mathrm{sf,mp}}=5$$ and $$\tilde{M}_{\mathrm{h}}=3000$$ successfully produces a $$z$$ ∼ 6 quasar with $$\sim 10^9\, {\rm M}_{\odot }$$ mass and ∼1047 erg s−1 luminosity. BH mergers play a crucial role at $$z$$ ≳ 9, causing an early boost in BH mass at a time when accretion-driven BH growth is negligible. With more stringent seeding conditions (e.g. $$\tilde{M}_{\mathrm{sf,mp}}=1000$$), the relative paucity of BH seeds results in a much lower merger rate. In this case, $$z$$ ≳ 6 quasars can only be formed if we enhance the maximum allowed BH accretion rates (by factors ≳10) compared to the accretion model used in IllustrisTNG. This can be achieved either by allowing for super-Eddington accretion, or by reducing the radiative efficiency. Our results demonstrate that progenitors of $$z$$ ∼ 6 quasars have distinct BH merger histories for different seeding models, which will be distinguishable with Laser Interferometer Space Antenna observations.
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Forming massive seed black holes in high-redshift quasar host progenitors
ABSTRACT The presence of massive black holes (BHs) with masses of the order of $$10^9\, {\rm M_\odot }$$, powering bright quasars when the Universe was less than 1 Gyr old, poses strong constraints on their formation mechanism. Several scenarios have been proposed to date to explain massive BH formation, from the low-mass seed BH remnants of the first generation of stars to the massive seed BHs resulting from the rapid collapse of massive gas clouds. However, the plausibility of some of these scenarios to occur within the progenitors of high-z quasars has not yet been thoroughly explored. In this work, we investigate, by combining dark-matter only N-body simulations with a semi-analytic framework, whether the conditions for the formation of massive seed BHs from synchronized atomic-cooling halo pairs and/or dynamically heated (DH) mini-haloes are fulfilled in the overdense regions where the progenitors of a typical high-redshift quasar host form and evolve. Our analysis shows that the peculiar conditions in such regions, i.e. strong halo clustering and high star formation rates, are crucial to produce a non-negligible number of massive seed BH host candidates: we find ≈1400 DH metal-free mini-haloes, including one of these which evolves to a synchronized pair and ends up in the massive quasar-host halo by z = 6. This demonstrates that the progenitors of high-redshift quasar host haloes can harbour early massive seed BHs. Our results further suggest that multiple massive seed BHs may form in or near the quasar host’s progenitors, potentially merging at lower redshifts and yielding gravitational wave events.
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- PAR ID:
- 10225595
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 503
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 5046 to 5060
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stab692
