Assessing inflow rates in atomic cooling haloes: implications for direct collapse black holes

Abstract

Supermassive black holes are not only common in the present-day galaxies, but billion solar masses black holes also powered z ≥ 6 quasars. One efficient way to form such black holes is the collapse of a massive primordial gas cloud into a so-called direct collapse black hole. The main requirement for this scenario is the presence of large accretion rates of ≥ 0.1 M ⊙ /yr to form a supermassive star. It is not yet clear how and under what conditions such accretion rates can be obtained. The prime aim of this work is to determine the mass accretion rates under non-isothermal collapse conditions. We perform high resolution cosmological simulations for three primordial halos of a few times 10 7 M ⊙ illuminated by an external UV flux, J 21 = 100 − 1000. We find that a rotationally supported structure of about parsec size is assembled, with an aspect ratio between 0.25−1 depending upon the thermodynamical properties. Rotational support, however, does not halt collapse, and mass inflow rates of ∼ 0.1 M ⊙ /yr can be obtained in the presence of even a moderate UV background flux of strength J 21 ≥ 100. To assess whether such large accretion rates can be maintained over longer time scales, we employed sink particles, confirming the persistence of accretion rates of ∼ 0.1 M ⊙ /yr. We propose that complete isothermal collapse and molecular hydrogen suppression may not always be necessary to form supermassive stars, precursors of black hole seeds. Sufficiently high inflow rates can be obtained for UV flux J 21 = 500 − 1000, at least for some cases. This value brings the estimate of the abundance of direct collapse black hole seeds closer to that high redshift quasars.

Blossoms from black hole seeds: properties and early growth regulated by supernova feedback

“…The only remaining coolant is atomic hydrogen, which cannot cool gas below ∼ 8000 K, thus leading to a very large Jeans mass of 10 5 M . In the very centre of a metal-free halo where molecular hydrogen formation is suppressed for at least 10 Myr (Visbal, Haiman & Bryan 2014;Latif & Volonteri 2015), and in the presence of large inflow rates (> 0.1 M /yr), a supermassive star can form, and from it a BH, retaining up to 90% of the stellar mass. This models predicts massive, but rare seeds, which can possibly explain the quasar population at z > 6 (Fan et al 2006;Jiang & et al, 2009;Mortlock et al 2011), but has more difficulties with accounting for the presence of BHs in almost all galaxies today (Habouzit et al 2016a).…”

The chemical evolution of self-gravitating primordial disks

“…In the context of supermassive stars, we emphasize that the majority of runs already started from an atomic gas, which typically remained atomic during the further evolution (e.g., Regan & Haehnelt 2009;Latif et al 2013a,c;Prieto et al 2013;Regan et al 2014;Becerra et al 2015). The longer-term evolution in the presence of molecular cooling has been explored in simulations by Latif et al (2014b) and Latif & Volonteri (2015). These simulations show that high accretion rates can be maintained, even though they do not resolve the scales considered here.…”

“…For instance, Begelman & Shlosman (2009) suggested that massive objects could also form from molecular gas in the presence of self-gravitating instabilities. Simulations by Latif et al (2014b) confirmed that massive objects of ∼10 3 −10 4 M still form for radiation fluxes below J crit , and accretion rates of ∼10 −1 M yr −1 can be maintained even for a moderate radiation background (Latif & Volonteri 2015). In addition, it is conceivable that an atomic gas forms through alternative pathways.…”

“…Even for more moderate radiation fluxes, massive stars with 10 3 −10 4 M may still form , and the rotational support in disks was found to increase for an increasing amount of molecular cooling (Latif & Volonteri 2015). Also, in this context, it is therefore important to understand the long-term evolution of self-gravitating disks both in the atomic and molecular cooling regime.…”

The Early Growth of the First Black Holes

“…Inayoshi & Haiman 2014;Latif & Volonteri 2015;Sakurai et al 2015a;Luo et al 2015), rapid gas infall appears to drive the expansion of the star episodically, limiting the emission of ionizing photons, as shown in Figure 2 (Sakurai et al 2015b). Likewise, high accretion rates are likely to be realized even in highly turbulent atomically-cooled collapsing gas (e.g.…”