Supermassive Black Hole Formation at High Redshifts via Direct Collapse: Physical Processes in the Early Stage

Abstract

We use numerical simulations to explore whether direct collapse can lead to the formation of supermassive black hole (SMBH) seeds at high redshifts. Using the adaptive mesh refinement code ENZO, we follow the evolution of gas within slowly tumbling dark matter (DM) halos of M vir ∼ 2 × 10 8 M and R vir ∼ 1 kpc. For our idealized simulations, we adopt cosmologically motivated DM and baryon density profiles and angular momentum distributions. Our principal goal is to understand how the collapsing flow overcomes the centrifugal barrier and whether it is subject to fragmentation which can potentially lead to star formation, decreasing the seed SMBH mass. We find that the collapse proceeds from inside out and leads either to a central runaway or to off-center fragmentation. A disk-like configuration is formed inside the centrifugal barrier, growing via accretion. For models with a more cuspy DM distribution, the gas collapses more and experiences a bar-like perturbation and a central runaway on scales of 1-10 pc. We have followed this inflow down to ∼10 −4 pc (∼10 AU), where it is estimated to become optically thick. The flow remains isothermal and the specific angular momentum, j, is efficiently transferred by gravitational torques in a cascade of nested bars. This cascade is triggered by finite perturbations from the large-scale mass distribution and by gas self-gravity, and supports a self-similar, disk-like collapse where the axial ratios remain constant. The mass accretion rate shows a global minimum on scales of ∼1-10 pc at the time of the central runaway. In the collapsing phase, virial supersonic turbulence develops and fragmentation is damped. Models with progressively larger initial DM cores evolve similarly, but the timescales become longer. In models with more organized initial rotation-when the rotation of spherical shells is constrained to be coplanar-a torus forms on scales ∼20-50 pc outside the disk, and appears to be supported by turbulent motions driven by accretion from the outside. The overall evolution of the models depends on the competition between two timescales, corresponding to the onset of the central runaway and of off-center fragmentation. In models with less organized rotation-when the rotation of spherical shells is randomized (but the total angular momentum remains unchanged)-the torus is greatly weakened, the central accretion timescale is shortened, and off-center fragmentation is suppressed-triggering the central runaway even in previously "stable" models. The resulting seed SMBH masses is found in the range M • ∼ 2 × 10 4 M -2 × 10 6 M , substantially higher than the mass range of Population III remnants. We argue that the above upper limit on M • appears to be more realistic, and lies close to the cutoff mass of detected SMBHs. Corollaries of this model include a possible correlation between SMBH and DM halo masses, and similarity between the SMBH and halo mass functions, at time of formation.

Unveiling the First Black Holes With JWST:Multi-wavelength Spectral Predictions

“…At these satellite sites, gas-rich proto-galactic disks could form that do not fragment or cool but rather go dynamically unstable (Q-unstable, see Toomre 1964), leading to rapid runaway accretion of gas to the center and to the formation of a massive DCBH seed. The physics and evolution of this process have been calculated analytically (Lodato & Natarajan 2006, 2007 and conducive conditions (assembly of massive proto-galactic disks) are increasingly seen to occur in state of the art high-resolution cosmological simulations of early structure formation (Regan & Haehnelt 2009;Choi et al 2013;Latif et al 2013). It is estimated that the typical masses of these DCBH seeds would lie in the range 10 4−5 M and the process is limited entirely by the gas reservoir (e.g.…”

Direct collapse to supermassive black hole seeds: comparing the AMR and SPH approaches

“…Direct collapse of isolated models with atomic gas has been performed and analysed by Choi et al (2013) for λ = 0.05, using Enzo. Many of the aspects of its evolution are generic.…”

“…For the second stage of the collapse to ensue, the gas must decouple from the background DM potential, i.e., its density must increase above the DM density at small radii (e.g., § 3.1 of Choi et al 2013Choi et al , 2015. In isolated models this is approximately the radius of the disk which forms behind the standing accretion shock.…”

Bright vigorous winds as signposts of supermassive black hole birth

“…Several possibilities have been discussed, c 2015 RAS such as the dissociation of H2 molecules by Lyman-Werner ionising radiation coming from nearby, star-forming galaxies in order to avoid cooling and fragmentation (Ferrara & Loeb 2013;Dijkstra, Ferrara & Mesinger 2014). Another possibility is the onset of supersonic turbulence and the removal of angular momentum due to non-axisymmetric perturbations and gravitational torques during the collapse of the halo (Begelman & Shlosman 2009;Choi, Shlosman & Begelman 2013, or at the centre of major merger remnants between rare and massive galaxies at high redshift (Mayer et al 2010(Mayer et al , 2015.…”