skip to main content

This content will become publicly available on April 1, 2023

Title: Supercritical growth pathway to overmassive black holes at cosmic dawn: coevolution with massive quasar hosts
Observations of the most luminous quasars at high redshifts (z > 6) have revealed that the largest supermassive black holes (SMBHs) at those epochs tend to be substantially overmassive relative to their host galaxies compared to the local relations, suggesting they experienced rapid early growth phases. We propose an assembly model for the SMBHs that end up in rare massive ∼ 1012 M⊙ host halos at z ∼ 6−7, applying a kinetic feedback prescription for BHs accreting above the Eddington rate, provided by radiation hydrodynamic simulations for the long-term evolution of the accretion-flow structure. The large inflow rates into these halos during their assembly enable the formation of > 109 M⊙ SMBHs by z ∼ 6, even starting from stellar-mass seeds at z ∼ 30, and even in the presence of outflows that reduce the BH feeding rate, especially at early times. This mechanism also naturally yields a high BH-to-galaxy mass ratio of > 0.01 before the SMBH mass reaches MBH > 109 M⊙ by z ∼ 6. These fast-growing SMBH progenitors are bright enough to be detected by upcoming observations with the James Webb Space Telescope over a wide range of redshift (7 < z < 15), regardless of more » how they were seeded. « less
Authors:
; ; ; ; ;
Award ID(s):
2006176
Publication Date:
NSF-PAR ID:
10337901
Journal Name:
The astrophysical journal
ISSN:
2041-8213
Sponsoring Org:
National Science Foundation
More Like this
  1. The existence of ∼10 9 M ⊙ supermassive black holes (SMBHs) within the first billion years of the Universe has stimulated numerous ideas for the prompt formation and rapid growth of black holes (BHs) in the early Universe. Here, we review ways in which the seeds of massive BHs may have first assembled, how they may have subsequently grown as massive as ∼10 9 M ⊙ , and how multimessenger observations could distinguish between different SMBH assembly scenarios. We conclude the following: ▪  The ultrarare ∼10 9 M ⊙ SMBHs represent only the tip of the iceberg. Early BHs likely fill a continuum from the stellar-mass (∼10M ⊙ ) to the supermassive (∼10 9 ) regimes, reflecting a range of initial masses and growth histories. ▪  Stellar-mass BHs were likely left behind by the first generation of stars at redshifts as high as ∼30, but their initial growth typically was stunted due to the shallow potential wells of their host galaxies. ▪  Conditions in some larger, metal-poor galaxies soon became conducive to the rapid formation and growth of massive seed holes, via gas accretion and by mergers in dense stellar clusters. ▪  BH masses depend on the environment (such asmore »the number and properties of nearby radiation sources and the local baryonic streaming velocity) and on the metal enrichment and assembly history of the host galaxy. ▪  Distinguishing between assembly mechanisms will be difficult, but a combination of observations by the Laser Interferometer Space Antenna (probing massive BH growth via mergers) and by deep multiwavelength electromagnetic observations (probing growth via gas accretion) is particularly promising.« less
  2. ABSTRACT Observations of massive galaxies at low redshift have revealed approximately linear scaling relations between the mass of a supermassive black hole (SMBH) and properties of its host galaxy. How these scaling relations evolve with redshift and whether they extend to lower-mass galaxies, however, remain open questions. Recent galaxy formation simulations predict a delayed, or ‘two-phase,’ growth of SMBHs: slow, highly intermittent BH growth due to repeated gas ejection by stellar feedback in low-mass galaxies, followed by more sustained gas accretion that eventually brings BHs on to the local scaling relations. The predicted two-phase growth implies a steep increase, or ‘kink,’ in BH-galaxy scaling relations at a stellar mass $\rm {M}_{*}\sim 5\times 10^{10}$ M⊙. We develop a parametric, semi-analytic model to compare different SMBH growth models against observations of the quasar luminosity function (QLF) at z ∼ 0.5−4. We compare models in which the relation between SMBH mass and galaxy mass is purely linear versus two-phase models. The models are anchored to the observed galaxy stellar mass function, and the BH mass functions at different redshifts are consistently connected by the accretion rates contributing to the QLF. The best fits suggest that two-phase evolution is significantly preferred by the QLFmore »data over a purely linear scaling relation. Moreover, when the model parameters are left free, the two-phase model fits imply a transition mass consistent with that predicted by simulations. Our analysis motivates further observational tests, including measurements of BH masses and active galactic nuclei activity at the low-mass end, which could more directly test two-phase SMBH growth.« less
  3. The existence of 109 M⊙ supermassive black holes (SMBHs) within the first billion years of the universe remains a puzzle in our conventional understanding of black hole formation and growth. The so-called direct-collapse scenario suggests that the formation of supermassive stars (SMSs) can yield the massive seeds of early SMBHs. This scenario leads to an overly massive BH galaxy (OMBG), whose nuclear black hole’s mass is comparable to or even greater than the surrounding stellar mass: a 104 − 106 M⊙ seed black hole is born in a dark matter halo with a mass as low as 107 − 108 M⊙. The black hole to stellar mass ratio is 𝑀bh/𝑀∗ ≫ 10−3, well in excess of the typical values at lower redshift. We investigate how long these newborn BHs remain outliers in the 𝑀bh − 𝑀∗ relation, by exploring the subsequent evolution of two OMBGs previously identified in the Renaissance simulations. We find that both OMBGs have𝑀bh/𝑀∗>1 during their entire life, from their birth at 𝑧≈15 until they merge with much more massive haloes at 𝑧 ≈ 8. We find that the OMBGs are spatially resolvable from their more massive, 1011 M⊙, neighboring haloes until their mergers are complete atmore »𝑧 ≈ 8. This affords a window for future observations with JWST and sensitive X-ray telescopes to diagnose the direct-collapse scenario, by detecting similar OMBGs and establishing their uniquely high black hole-to-stellar mass ratio.« less
  4. 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, $z$more »≳ 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.

    « less
  5. ABSTRACT

    The mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) is probing supermassive black holes (SMBHs) in galaxies across the Hubble sequence via molecular gas dynamics. We present the first WISDOM study of a luminous infrared galaxy with an active galactic nuclei (AGNs): Fairall 49. We use new ALMA observations of the CO(2 − 1) line with a spatial resolution of ∼80 pc together with ancillary HST imaging. We reach the following results: (1) The CO kinematics are well described by a regularly rotating gas disc with a radial inflow motion, suggesting weak feedback on the cold gas from both AGN and starburst activity; (2) The dynamically inferred SMBH mass is 1.6 ± 0.4(rnd) ± 0.8(sys) × 108 M⊙ assuming that we have accurately subtracted the AGN and starburst light contributions, which have a luminosity of ∼109 L⊙; (3) The SMBH mass agrees with the SMBH−stellar mass relation but is ∼50 times higher than previous estimates from X-ray variability; (4) The dynamically inferred molecular gas mass is 30 times smaller than that inferred from adopting the Galactic CO-to-H2 conversion factor (XCO) for thermalized gas, suggesting low values of XCO; (5) the molecular gas inflow rate increases steadily with radius and may be as high as ∼5 M⊙ yr−1. This work highlights themore »potential of using high-resolution CO data to estimate, in addition to SMBH masses, the XCO factor, and gas inflow rates in nearby galaxies.

    « less