John A. Regan

Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures ≳10 000 K

Large dynamic range numerical simulations of atomic cooling driven collapse of gas in pre-galactic dark matter haloes with T vir ∼ 10 000 K show that the gas loses 90 per cent and more of its angular momentum before rotational support sets in. In a fraction of these haloes where the metallicity is low and ultraviolet (UV) radiation suppresses H 2 cooling, conditions are thus very favourable for the rapid build-up of massive black holes. Depending on the progression of metal enrichment, the continued suppression of H 2 cooling by external and internal UV radiation and the ability to trap the entropy produced by the release of gravitational energy, the gas at the centre of the halo is expected to form a supermassive star, a stellar-mass black hole accreting at super-Eddington accretion rates or a compact star-cluster undergoing collisional run-away of massive stars at its centre. In all three cases, a massive black hole of initially modest mass finds itself at the centre of a rapid inflow of gas with inflow rates of ≥1 M ⊙ yr ―1 . The massive black hole will thus grow quickly to a mass of 10 5 ― 10 6 M ⊙ until further inflow is halted either by consumption of gas by star formation or by the increasing energy and momentum feedback from the growing massive black hole. Conditions for the formation of massive seed black holes in this way are most favourable in haloes with T vir ∼ 15 000 K and V vir ∼ 20 km s ―1 with less massive haloes not allowing collapse of gas by atomic cooling and more massive haloes being more prone to fragmentation. This should imprint a characteristic mass on the mass spectrum of an early population of massive black hole seeds in pre-galactic haloes which will later grow into the observed population of supermassive black holes in galactic bulges.

The formation of compact massive self-gravitating discs in metal-free haloes with virial temperatures of ∼13 000–30 000 K

We have used the hydrodynamical adaptive mesh refinement code ENZO to investigate the dynamical evolution of the gas at the centre of dark matter haloes with virial velocities of ∼20-30 km s -1 and virial temperatures of ∼ 13 000-30 000K at z ∼ 15 in a cosmological context. The virial temperature of the dark matter haloes is above the threshold where atomic cooling by hydrogen allows the gas to cool and collapse. We neglect cooling by molecular hydrogen and metals, as may be plausible if H 2 cooling is suppressed by a metagalactic Lyman-Werner background or an internal source of Lyman-Werner photons, and metal enrichment has not progressed very far. The gas in the haloes becomes gravitationally unstable and develops turbulent velocities comparable to the virial velocities of the dark matter haloes. Within a few dynamical times, it settles into a nearly isothermal density profile over many decades in radius losing most of its angular momentum in the process. About 0.1-1 per cent of the baryons, at the centre of the dark matter haloes, collapse into a self-gravitating, fat, ellipsoidal, centrifugally supported exponential disc with scalelength of ∼0.075-0.27 pc and rotation velocities of 25-60 km s -1 . We are able to follow the settling of the gas into centrifugal support and the dynamical evolution of the compact disc in each dark matter halo for a few dynamical times. The dynamical evolution of the gas at the centre of the haloes is complex. In one of the haloes, the gas at the centre fragments into a triple system leading to strong tidal perturbations and eventually to the infall of a secondary smaller clump into the most massive primary clump. The formation of centrifugally supported self-gravitating massive discs is likely to be an important intermediary stage en route to the formation of a massive black hole seed.

Numerical resolution effects on simulations of massive black hole seeds

We have performed high-resolution numerical simulations with the hydrodynamical AMR code ENZO to investigate the formation of massive seed black holes in a sample of six dark matter haloes above the atomic cooling threshold. The aim of this study is to illustrate the effects of varying the maximum refinement level on the final ob ject formed. The virial temperatures of the simulated haloes range from T ∼ 10000 K− 16000 K and they have virial masses in the range M ∼ 2× 10 7 M⊙ to M ∼ 7× 10 7 M⊙ at z ∼ 15. The outcome of our six fiducial simulations is both generic and robust. A rotationa lly supported, marginally gravitationally stable, disk forms with an exponential profile. The mass and scale length of this disk depends strongly on the maximum refinement level used. Varyi ng the maximum refinement level by factors between 1/64 to 256 times the fiducial level illustrates the care that mu st be taken in interpreting the results. The lower resolution sim ulations show tentative evidence that the gas may become rotationally supported out to 20 pc while the highest resolution simulations show only weak evidence of rotational support due to the shorter dynamical times for which the simulation runs. The higher resolution simulations do, however, point to fragmentation at small scales of the order of ∼ 100 AU. In the highest resolution simulations a central object of a few times 10 2 M⊙ forms with multiple strongly bound, Jeans unstable, clumps of ≈ 10 M⊙ and radii of 10 - 20 AU suggesting the formation of dense star clusters in these haloes.

The Direct Collapse of a Massive Black Hole Seed under the Influence of an Anisotropic Lyman-Werner Source

The direct collapse model of supermassive black hole seed formation provides an attractive solution to the origin of the quasars now routinely observed at

Numerical simulations of the Lyman α forest – a comparison of gadget‐2 and enzo

z \gtrsim 6

The Sherwood simulation suite: overview and data comparisons with the Lyman α forest at redshifts 2 ≤ z ≤ 5

. We use the adaptive mesh refinement code Enzo to simulate the collapse of gas at high redshift, including a nine species chemical model of H, He, and H

GRACKLE: a chemistry and cooling library for astrophysics

_2

Positive or negative? The impact of X-ray feedback on the formation of direct collapse black hole seeds

. The direct collapse model requires that the gas cools predominantly via atomic hydrogen. To this end we simulate the effect of an anisotropic radiation source on the collapse of a halo at high redshift. The radiation source is placed at a distance of 3 kpc (physical) from the collapsing object. The source is set to emit monochromatically in the center of the Lyman-Werner (LW) band only at

The effect of dark matter resolution on the collapse of baryons in high-redshift numerical simulations

12.8 \ \rm{eV}

Music from the heavens - Gravitational waves from supermassive black hole mergers in the EAGLE simulations

. The LW radiation emitted from the high redshift source is followed self-consistently using ray tracing techniques. We find that, due to self-shielding, a small amount of H