Seeds Of Supermassive Black Holes Research Articles

Supermassive black holes triggered by QCD axion bubbles

Supermassive black holes (SMBHs) are ubiquitous in the center of galaxies, although the origin of their massive seeds is still unknown. In this paper, we investigate the formation of SMBHs from the quantum chromodynamics (QCD) axion bubbles. In this case, primordial black holes (PBHs) are considered as the seeds of SMBHs, which are generated from the QCD axion bubbles due to an explicit Peccei–Quinn (PQ) symmetry breaking after inflation. The QCD axion bubbles are formed when the QCD axion starts to oscillate during the QCD phase transition. We consider a general case in which the axion bubbles are formed with the bubble effective angle θ eff ∈ (0, π], leading to the minimum PBH mass ∼O(104−107)M⊙ for the axion decay constant fa∼O(1016)GeV . The PBHs at this mass region may account for the seeds of SMBHs.

Structure formation with primordial black holes to alleviate early star formation tension revealed by JWST

This Letter explores the potential role of primordial black holes (PBHs) to address cosmological tensions as the presence of more massive than expected galaxies at high redshifts, as indicated by recent James Webb Space Telescope observations. Motivated by inflation models that enhance the power at scales beyond the observable range that produce PBHs with Schechter-like mass functions, we aim to explain the excess of high redshift galaxies via a modification of the Lambda cold dark matter power spectrum that consists in adding (i) a blue spectral index $n_b$ at $k_ piv =10/$Mpc and (ii) Poisson and isocurvature contributions from massive PBHs that only make up $0.5<!PCT!>$ of the dark matter. We simulated these models using the SWIFT code and find an increased abundance of high redshift galaxies in simulations that include PBHs. We compared these models to estimates from James Webb Space Telescope observations. Unlike the Lambda cold dark matter model, the inclusion of PBHs allowed us to reproduce the the observations with reasonable values for the star formation efficiency. Furthermore, the power spectra we adopted potentially produce PBHs that can serve as seeds for supermassive black holes with masses $7.57 odot

Representing low-mass black hole seeds in cosmological simulations: A new sub-grid stochastic seed model

ABSTRACT The physical origin of the seeds of supermassive black holes (SMBHs), with postulated initial masses ranging from ∼105 M⊙ to as low as ∼102 M⊙, is currently unknown. Most existing cosmological hydrodynamic simulations adopt very simple, ad hoc prescriptions for BH seeding and seed at unphysically high masses ∼105–106 M⊙. In this work, we introduce a novel sub-grid BH seeding model for cosmological simulations that is directly calibrated to high-resolution zoom simulations that explicitly resolve ∼103 M⊙ seeds forming within haloes with pristine, dense gas. We trace the BH growth along galaxy merger trees until their descendants reach masses of ∼104 or 105 M⊙. The results are used to build a new stochastic seeding model that directly seeds these descendants in lower resolution versions of our zoom region. Remarkably, we find that by seeding the descendants simply based on total galaxy mass, redshift and an environmental richness parameter, we can reproduce the results of the detailed gas-based seeding model. The baryonic properties of the host galaxies are well reproduced by the mass-based seeding criterion. The redshift-dependence of the mass-based criterion captures the combined influence of halo growth, dense gas formation, and metal enrichment on the formation of ∼103 M⊙ seeds. The environment-based seeding criterion seeds the descendants in rich environments with higher numbers of neighbouring galaxies. This accounts for the impact of unresolved merger dominated growth of BHs, which produces faster growth of descendants in richer environments with more extensive BH merger history. Our new seed model will be useful for representing a variety of low-mass seeding channels within next-generation larger volume uniform cosmological simulations.

UNCOVER: A NIRSpec Identification of a Broad-line AGN at z = 8.50

Deep observations with the James Webb Space Telescope (JWST) have revealed an emerging population of red pointlike sources that could provide a link between the postulated supermassive black hole seeds and observed quasars. In this work, we present a JWST/NIRSpec spectrum from the JWST Cycle 1 UNCOVER Treasury survey of a massive accreting black hole at z = 8.50 displaying a clear broad-line component as inferred from the Hβ line with FWHM = 3439 ± 413 km s−1, typical of the broad-line region of an active galactic nucleus (AGN). The AGN nature of this object is further supported by high ionization, as inferred from emission lines, and a point-source morphology. We compute a black hole mass of and a bolometric luminosity of L bol ∼ 6.6 × 1045 erg s−1. These values imply that our object is accreting at ∼40% of the Eddington limit. Detailed modeling of the spectral energy distribution in the optical and near-infrared, together with constraints from ALMA, indicate an upper limit on the stellar mass of , which would lead to an unprecedented ratio of black hole to host mass of at least ∼30%. This is orders of magnitude higher compared to the local QSOs but consistent with recent AGN studies at high redshift with JWST. This finding suggests that a nonnegligible fraction of supermassive black holes either started out from massive seeds and/or grew at a super-Eddington rate at high redshift. Given the predicted number densities of high-z faint AGN, future NIRSpec observations of larger samples will allow us to further investigate galaxy–black hole coevolution in the early Universe.

Direct Collapse to Precursors of Supermassive Black Hole Seeds: Radiation-feedback-generated Outflows

We use high-resolution zoom-in cosmological simulations to model outflow triggered by radiation and thermal drivers around the central mass accumulation during direct collapse within the dark matter (DM) halo. The maximal resolution is 1.3 × 10−5 pc, and no restrictions are put on the geometry of the inflow/outflow. The central mass is considered prior to the formation of the supermassive black hole seed at a redshift of z ∼ 15.9 and can constitute either a supermassive star (SMS) of ∼105 M ⊙ surrounded by a growing accretion disk or a self-gravitating disk. The radiation transfer is modeled using the ray-tracing algorithm. Due to the high accretion rate of ∼1 M ⊙ yr−1 determined by the DM halo, accretion is mildly supercritical, resulting in mildly supercritical luminosity that has only a limited effect on the accretion rate, with a duty cycle of ∼0.9. We observe a fast development of hot cavities, which quickly extend into polar funnels and expand dense shells. Within the funnels, fast winds, ∼103 km s−1, are mass-loaded by the accreting gas. We follow the expanding shells to ∼1 pc, when the shell velocity remains substantially (∼5 times) above the escape speed. The ionization cones formed by the central UV/X-ray completely ionize the cavities. Extrapolating the outflow properties shows that the halo material outside the shell will have difficulty stopping it. We therefore conclude that the expanding wind-driven shell will break out of the central parsec and will reach the halo virial radius. Finally, the anisotropic accretion flow on subparsec scales will attenuate the UV/soft X-rays on the H2. Hence, the formation of funnels and powerful outflows around, e.g., SMSs can have interesting observational corollaries.

Supermassive black hole seeds from sub-keV dark matter

Quasars observed at redshifts z ∼ 6–7.5 are powered by supermassive black holes which are too large to have grown from early stellar remnants without efficient super-Eddington accretion. A proposal for alleviating this tension is for dust and metal-free gas clouds to have undergone a process of direct collapse, producing black hole seeds of mass M seed ∼ 105 M ⊙ around redshift z ∼ 17. For direct collapse to occur, a large flux of UV photons must exist to photodissociate molecular hydrogen, allowing the gas to cool slowly and avoid fragmentation. We investigate the possibility of sub-keV mass dark matter decaying or annihilating to produce the UV flux needed to cause direct collapse. To do so, we calculate the produced UV flux from dark matter annihilations and decays within the gas cloud's halo and compare these to the requirements of the UV spectrum found by previous hydrodynamical simulations. We find that annihilating dark matter with a mass in the range of 13.6 eV ≤ mdm ≤ 20 eV can produce the required flux while avoiding existing constraints. A non-thermally produced dark matter particle which comprises the entire dark matter abundance requires a thermally averaged cross section of 〈σv〉 ∼ 10-35 cm3/s. Alternatively, the flux could originate from a thermal relic which comprises only a fraction ∼ 10-9 of the total dark matter density. Decaying dark matter models which are unconstrained by independent astrophysical observations are unable to sufficiently suppress molecular hydrogen, except in gas clouds embedded in dark matter halos which are larger, cuspier, or more concentrated than current simulations predict. Lastly, we explore how our results could change with the inclusion of full three-dimensional effects. Notably, we demonstrate that if the H2 self-shielding is less than the conservative estimate used in this work, the range of both annihilating and decaying dark matter models which can cause direct collapse is significantly increased.

3D Radiation-hydrodynamic Simulations Resolving Interior of Rapidly Accreting Primordial Protostar

Direct collapse of supermassive stars is a possible pathway to form supermassive black hole seeds at high redshifts. Whereas previous three-dimensional (3D) simulations demonstrate that supermassive stars form via rapid mass accretion, those resolving the stellar interior have been limited. Here, we report 3D radiation-hydrodynamic (RHD) simulations following the evolution of rapidly accreting protostars resolving the stellar interior. We use an adaptive mesh refinement code with our newly developed RHD solver employing an explicit M1 closure method. We follow the early evolution until the stellar mass reaches ∼10 M ⊙ from two different initial configurations of spherical and turbulent clouds. We demonstrate that, in both cases, a swollen protostar whose radius is 100–1000 R ⊙ appears, as predicted by the stellar evolution calculations. Its effective temperature remains a few thousand Kelvin, and the radiative feedback by ionizing photons is too weak to disturb the accretion flow up to the epoch examined in this work. In the turbulent case, the protostar rotates rapidly at more than 0.4 times the Keplerian velocity owing to the angular momentum provided by the initial turbulence. The protostar approximates an oblate spheroid, and its equatorial radius is more than twice the polar radius. Our results suggest that we need to consider the rapid stellar rotation to elucidate the realistic 3D protostellar evolution in the supermassive star formation.

On the growth of supermassive black holes formed from the gravitational collapse of fermionic dark matter cores

ABSTRACT Observations support the idea that supermassive black holes (SMBHs) power the emission at the centre of active galaxies. However, contrary to stellar-mass BHs, there is a poor understanding of their origin and physical formation channel. In this article, we propose a new process of SMBH formation in the early Universe that is not associated with baryonic matter (massive stars) or primordial cosmology. In this novel approach, SMBH seeds originate from the gravitational collapse of fermionic dense dark matter (DM) cores that arise at the centre of DM haloes as they form. We show that such a DM formation channel can occur before star formation, leading to heavier BH seeds than standard baryonic channels. The SMBH seeds subsequently grow by accretion. We compute the evolution of the mass and angular momentum of the BH using a geodesic general relativistic disc accretion model. We show that these SMBH seeds grow to ∼109–$10^{10} \, \mathrm{M}_\odot$ in the first Gyr of the lifetime of the Universe without invoking unrealistic (or fine-tuned) accretion rates.

The most massive Population III stars

ABSTRACT Recent data from the JWST suggest that there are realistic prospects for detecting the earliest generation of stars at redshift ∼20. These metal-poor, gaseous Population III (Pop III) stars are likely in the mass range $10\!-\!10^3\, {\rm M}_{\odot }$ . We develop a framework for calculating the abundances of Pop III stars as well as the distribution of the most massive Pop III stars based on an application of extreme-value statistics. Our calculations use the star formation rate density from a recent simulation to calibrate the star formation efficiency from which the Pop III stellar abundances are derived. Our extreme-value modelling suggests that the most massive Pop III stars at redshifts 10 < z < 20 are likely to be $\gtrsim 10^3\!-\!10^4\, {\rm M}_\odot$ . Such extreme Pop III stars were sufficiently numerous to be the seeds of supermassive black holes at high redshifts and possibly source detectable gravitational waves. We conclude that the extreme-value formalism provides an effective way to constrain the stellar initial mass function.

Multiflavour SMBH seeding and evolution in cosmological environments

ABSTRACT We study the genesis and evolution of supermassive black hole (SMBH) seeds through different formation channels, from PopIII remnants to massive seeds, modelled within the L-Galaxies semi-analytic code. We run the model on the Millennium-II simulation (MR-II) merger trees, as their halo-mass resolution ($M_{\rm vir,res} \sim 10^7\, \mathrm{M}_\odot \, h^{-1}$) allows to study in a cosmological volume ($L_{\rm box}=100\, \mathrm{Mpc}\, h^{-1}$) the evolution of atomic-cooling haloes ($T_{\rm vir} \gtrsim 10^4\, \mathrm{K}$) where intermediate-mass and heavy seeds are expected to form. We track the formation of these seeds according to spatial variations of the chemical and radiative feedback of star formation. Not being able to resolve the first mini-haloes ($T_{\rm vir} \sim 10^3\, \mathrm{K}$), we inherit evolved PopIII remnants in a sub-grid fashion, using the results of the GQd model. We also include the formation of heavy seeds in gas-rich massive mergers, which are very rare in the MR-II volume. The descendants of light seeds numerically prevail among our SMBHs population at all masses and z. Heavier seeds form in dense environments where close neighbours provide the required UV illumination. Overall, our model produces a z = 0 SMBHs population whose statistical properties meet current constraints. We find that the BH occupation fraction highly depends on the seeding efficiency and that the scaling relation between BH and stellar mass, in the dwarf-mass regime, is flatter than in the high-mass range. Finally, a fraction of BHs hosted in local dwarf galaxies never grow since they form at z > 6.

Radiative feedback on supermassive star formation: the massive end of the Population III initial mass function

ABSTRACT Supermassive stars with masses of M* ≃ 104–105 M⊙ are invoked as possible seeds of high-redshift supermassive black holes, but it remains under debate whether their protostar indeed acquires sufficient mass via gas accretion overcoming radiative feedback. We investigate protostellar growth in dynamically heated atomic cooling haloes (ACHs) found in recent cosmological simulations, performing three-dimensional radiation hydrodynamical simulations that consider stellar evolution under variable mass accretion. We find that one of the ACHs feeds the central protostar at rates exceeding a critical value, above which the star evolves in a cool bloating phase and hardly produces ionizing photons. Consequently, the stellar mass reaches M* ≳ 104 M⊙ unimpeded by radiative feedback. In the other ACH, where the mass supply rate is lower, the star evolves almost as a hot main-sequence star, emitting intense ionizing radiation. Then, the stellar mass growth is terminated around 500 M⊙ by photoevaporation of the circumstellar disc. Our simulations provide a formula of the final stellar mass determined either by stellar feedback or their lifetime as a function of the mass supply rate from the parent cloud. Combining the results with the statistical properties of star-forming clouds in high-redshift quasar progenitor haloes, we construct a top-heavy mass distribution of primordial stars over M* ≃ 100–105 M⊙, approximately following a power-law spectrum of ${\propto} M_\ast ^{-1.3}$. Their black hole remnants would be further fed via the dense debris disc, powering ‘milliquasars’ with a bolometric luminosity of Lbol ≳ 1043 erg s−1.

Cosmological 21-cm line observations to test scenarios of super-Eddington accretion on to black holes being seeds of high-redshifted supermassive black holes

In this paper, we study scenarios of the super-Eddington accretion onto black holes at high redshifts $z > 10$, which are expected to be seeds to evolve to supermassive black holes until redshift $z \sim 7$. For an initial mass, $M_{\rm BH, ini} \lesssim 2 \times 10^{3} M_{\odot}$ of a seed BH, we definitely need the super-Eddington accretion, which can be applicable to both astrophysical and primordial origins. Such an accretion disk inevitably emitted high-energy photons which had heated the cosmological plasma of the inter-galactic medium continuously from high redshifts. In this case, the cosmic history of cosmological gas temperature is modified, by which the absorption feature of the cosmological 21 cm lines is suppressed. By comparing theoretical predictions of the 21cm line absorption with the observational data at $z\sim17$, we obtain a cosmological upper bound on the mass-accretion rate as a function of the seed BH masses. In order to realize $M_{\rm BH} \sim 10^9 M_{\odot}$ at $z \sim 7$ by a continuous mass-accretion on to a seed BH, to be consistent with the cosmological 21cm line absorption at $z \sim 17$, we obtained an severe upper bound on the initial mass of the seed BH to be $M_{\rm BH, ini} \lesssim 10^2 M_{\odot}$ ($M_{\rm BH, ini} \lesssim 10^6 M_{\odot}$) when we assume a seed BH with its comoving number density $n_{\rm seed,0} \sim 10^{-3} {\rm Mpc}^{-3}$ ($n_{\rm seed,0} \sim 10^{-7} {\rm Mpc}^{-3}$). We also discuss some implications for application to primordial black holes as the seed black holes.

Implications of stochastic effects for primordial black hole production in ultra-slow-roll inflation

We study the impact of stochastic noise on the generation of primordial black hole (PBH) seeds in ultra-slow-roll (USR) inflation with numerical simulations. We consider the non-linearity of the system by consistently taking into account the noise dependence on the inflaton perturbations, while evolving the perturbations on the coarse-grained background affected by the noise. We capture in this way the non-Markovian nature of the dynamics, and demonstrate that non-Markovian effects are subleading. Using the ΔN formalism, we find the probability distribution P(ℛ) of the comoving curvature perturbation ℛ. We consider inflationary potentials that fit the CMB and lead to PBH dark matter with i) asteroid, ii) solar, or iii) Planck mass, as well as iv) PBHs that form the seeds of supermassive black holes. We find that stochastic effects enhance the PBH abundance by a factor of \U0001d4aa(10)–\U0001d4aa(108), depending on the PBH mass. We also show that the usual approximation, where stochastic kicks depend only on the Hubble rate, either underestimates or overestimates the abundance by orders of magnitude, depending on the potential. We evaluate the gauge dependence of the results, discuss the quantum-to-classical transition, and highlight open issues of the application of the stochastic formalism to USR inflation.

Structure of the super-Eddington outflow and its impact on the cosmological scale

Abstract It is one of the biggest issues in black hole (BH) astrophysics how to evaluate BH feedback to its environments precisely. Aiming at studying the unique gas dynamics of super-Eddington flow around supermassive black hole (SMBH) seeds at high redshift, we carried out axisymmetric two-dimensional radiation hydrodynamic simulations using a nested simulation-box method. Here we divide the simulation box into an inner zone at (2–3 × 103)rSch (with rSch being the Schwarzschild radius) and an outer zone at (2 × 103–3 × 106)rSch, with smooth connection of the physical quantities, such as gas density, velocity, and radiation energy. We start the calculation by injecting mass through the outer boundary of the inner zone at a constant rate of $\dot{M}_{\rm {inj}}=10^3L_{\rm {Edd}}/c^2$, where LEdd is the Eddington luminosity and c is the speed of light. A powerful outflow is generated in the innermost region and it propagates from the inner zone to the outer zone. The outflows are characterized by a velocity of 0.02c (0.7c) and density of 10−17 (10−19) g cm−3 for near the edge-on (face-on) direction. The outflow is gradually accelerated as it travels by accepting radiation-pressure force. The final mass outflow rate at the outermost boundary is $\dot{M}_{\rm {out}}\sim 0.3 \times \dot{M}_{\rm {inj}}$. By extrapolating the outflow structure to a further larger scale, we find that the momentum and energy fluxes at r ∼ 0.1 pc are ∼10–100 LEdd/c and ∼0.1–10 LEdd, respectively. Moreover, we find that the impacts are highly anisotropic, in the sense that larger impacts occur towards the face-on direction than in the edge-on direction. These results indicate that the BH feedback will work more efficiently on the interstellar medium than assumed in the cosmological simulations.

Primordial black holes from spectator field bubbles

We study the evolution of light spectator fields in an asymmetric polynomial potential. During inflation, stochastic fluctuations displace the spectator field from the global minimum of its potential, populating the false vacuum state and thereby allowing for the formation of false vacuum bubbles. By using a lattice simulation, we show that these bubbles begin to contract once they re-enter the horizon and, if sufficiently large, collapse into black holes. This process generally results in the formation of primordial black holes, which, due to the specific shape of their mass function, are constrained to yield at most 1% of the total dark matter abundance. However, the resulting population can source gravitational wave signals observable at the LIGO-Virgo experiments, provide seeds for supermassive black holes or cause a transient matter-dominated phase in the early Universe.

Nucleosynthetic signatures of primordial origin around supermassive black holes

If primordial black holes (PBHs) seeded the supermassive black holes (SMBHs) at the centers of high-redshift quasars, then the gas surrounding these black holes may reveal nucleosynthetic clues to their primordial origins. We present predictions of altered primordial abundances around PBHs massive enough to seed SMBHs at z~6-7.5. We find that if PBHs with initial masses of ~10^5 M$_{\odot}$ are responsible for such SMBHs, they may produce primordial Deuterium and Helium fractions enhanced by >~ 10%, and Lithium abundance depleted by >~10%, at distances of up to ~ a comoving kiloparsec away from the black hole after decoupling. We estimate that ~ 10^8 M$_{\odot}$ of gas is enhanced (or depleted) by at least one percent. Evidence of these modified primordial Deuterium, Helium, and Lithium abundances could still be present if this circum-PBH gas remains unaccreted by the SMBH and in or near the host galaxies of high-redshift quasars. Measuring the abundance anomalies will be challenging, but could offer a novel way to reveal the primordial origin of such SMBH seeds.

Supermassive stars with random transverse magnetic fields

ABSTRACT Gravitational dynamic collapses of supermassive stars (SMSs) triggered at certain critical stages may give rise to black holes (BHs) in a broad mass range that populate the Universe including the early Universe. SMSs have been speculated as the progenitors or seeds of supermassive BHs that power quasars and active galactic nuclei. We study quasi-spherical magnetostatic equilibria and magnetohydrodynamic (MHD) radial pulsational (in)stability properties of non-rotating SMSs involving random transverse magnetic fields (RTMFs) using the general relativity (GR). With RTMFs, the maxima of the gravitational binding energy mark the GR MHD transition from stability to instability and the RTMF does not modify the GR stability criterion significantly when the ratio ${\cal M}/\left|\Omega \right|\lesssim0.1$, where $\cal M$ is the total magnetic energy and Ω is the total gravitational potential energy. When $0.1\lesssim{\cal M}/\left|\Omega \right|\lesssim1$, nevertheless, the critical GR magnetostatic equilibria on the verge of GR MHD collapses or explosions may change drastically, raising the upper mass limit at the onset of GR MHD instability from ∼105 to ∼106 M⊙ and even higher. For ${\cal M}/\left|\Omega \right|\sim 1$, the evolution track of magnetized SMS is shifted towards the redder part of the Hertzsprung–Russell diagram, featuring a sort of ‘magnetic reddening’ associated with the stellar ‘magnetized envelope inflation’. By estimates, the RTMF energy stored in an SMS can be as large as ∼1057 erg, enough to power gamma-ray bursts, fast radio bursts, or other forms of powerful electromagnetic wave bursts. It is possible for magnetized massive stars to dynamically form BHs in the mass range from several tens to thousands of solar masses without necessarily triggering the central electron-positron e± instability inside such stars – this fact is highly pertinent to the reports of LIGO-Virgo gravitational wave event scenario of binary BH mergers.

Evolution of High-redshift Quasar Hosts and Promotion of Massive Black Hole Seed Formation

Abstract High-redshift luminous quasars powered by accreting supermassive black holes (SMBHs) with mass ≳109 M ⊙ constrain their formation pathways. We investigate the formation of heavy seeds of SMBHs through gas collapse in the quasar host progenitors, using merger trees to trace the halo growth in highly biased, overdense regions of the universe. The progenitor halos are likely irradiated by intense H2-photodissociating radiation from nearby star-forming galaxies and heat the interior gas by successive mergers. The kinetic energy of the gas originating from mergers, as well as the baryonic streaming motion, prevents gas collapse and delays prior star formation. With a streaming velocity higher than the rms value, gas clouds in nearly all 104 realizations of merger trees enter the atomic-cooling stage and begin to collapse isothermally with T ≃ 8000 K via Lyα cooling. The fraction of trees that host isothermal gas collapse is 14% and increases with streaming velocity, while the rest form H2-cooled cores after short isothermal phases. If the collapsing gas is enriched to Z crit ∼ 2 × 10−3 Z ⊙, requiring efficient metal mixing, this fraction could be reduced by additional cooling via metal fine-structure lines. In the massive collapsing gas, the accretion rate onto a newly born protostar ranges between 3 × 10−3 M ⊙ yr−1 and 5 M ⊙ yr−1, among which a large fraction exceeds the critical rate suppressing stellar radiative feedback. As a result, we expect a distribution of stellar mass (presumably BH mass) ranging from several hundred to above 105 M ⊙, potentially forming massive BH binary mergers and yielding gravitational-wave events.

SMBH seeds from dissipative dark matter

The existence of supermassive black holes (SMBHs) with masses greater than ∼ 109 M ☉ at high redshift (z ≳ 7) is difficult to accommodate in standard astrophysical scenarios. We study the possibility that (nearly) totally dissipative self-interacting dark matter (tdSIDM)–in rare, high density dark matter fluctuations in the early Universe — produces SMBH seeds through catastrophic collapse. We use a semi-analytic model, tested and calibrated by a series of N-body simulations of isolated dark matter halos, to compute the collapse criteria and timescale of tdSIDM halos, where dark matter loses nearly all of its kinetic energy in a single collision in the center-of-momentum frame. Applying this model to halo merger trees, we empirically assign SMBH seeds to halos and trace the formation and evolution history of SMBHs. We make predictions for the quasar luminosity function, the M BH-σv * relation, and cosmic SMBH mass density at high redshift and compare them to observations. We find that a dissipative dark matter interaction cross-section of σ/m ∼ 0.05 cm2/g is sufficient to produce the SMBHs observed in the early Universe while remaining consistent with ordinary SMBHs in the late Universe.

Light, medium-weight, or heavy? The nature of the first supermassive black hole seeds

ABSTRACT Observations of hyper-luminous quasars at z>6 reveal the rapid growth of supermassive black holes (SMBHs ${\gt}10^9 \,\rm M_{\odot }$) whose origin is still difficult to explain. Their progenitors may have formed as remnants of massive, metal-free stars (light seeds), via stellar collisions (medium-weight seeds) and/or massive gas clouds direct collapse (heavy seeds). In this work, we investigate for the first time the relative role of these three seed populations in the formation of z>6 SMBHs within an Eddington-limited gas accretion scenario. To this aim, we implement in our semi-analytical data-constrained model a statistical description of the spatial fluctuations of Lyman–Werner (LW) photodissociating radiation and of metal/dust enrichment. This allows us to set the physical conditions for black hole seeds formation, exploring their relative birth rate in a highly biased region of the Universe at z>6. We find that the inclusion of medium-weight seeds does not qualitatively change the growth history of the first SMBHs: although less massive seeds (${\lt}10^3\, \rm M_\odot$) form at a higher rate, the mass growth of a ${\sim}10^9\, \rm M_\odot$ SMBH at z<15 is driven by efficient gas accretion (at a sub-Eddington rate) on to its heavy progenitors ($10^5\, \rm M_\odot$). This conclusion holds independently of the critical level of LW radiation and even when medium-weight seeds are allowed to form in higher metallicity galaxies, via the so-called supercompetitive accretion scenario. Our study suggests that the genealogy of z∼6 SMBHs is characterized by a rich variety of BH progenitors, which represent only a small fraction (${\lt} 10{-}20{{\ \rm per\ cent}}$) of all the BHs that seed galaxies at z>15.