Impact of dust cooling on direct collapse black hole formation

TL;DR

This study investigates how trace amounts of dust and metals influence the formation of direct collapse black holes in primordial halos, revealing that dust cooling affects gas temperature, fragmentation, and inflow rates, thus impacting black hole seed formation.

Contribution

It provides the first detailed cosmological simulations showing dust cooling's role in direct collapse black hole formation at very low metallicities.

Findings

Dust cooling lowers gas temperature at high densities.

No bound clumps form at metallicities below 10^{-5} Z_sun.

High inflow rates (~0.1 M_sun/yr) can lead to massive black hole seeds.

Abstract

Observations of quasars at $ z > 6$ suggest the presence of black holes with a few times $\rm 10^9 ~M_{\odot}$. Numerous models have been proposed to explain their existence including the direct collapse which provides massive seeds of $\rm 10^5~M_{\odot}$. The isothermal direct collapse requires a strong Lyman-Werner flux to quench $\rm H_2$ formation in massive primordial halos. In this study, we explore the impact of trace amounts of metals and dust enrichment. We perform three dimensional cosmological simulations for two halos of $\rm > 10^7~M_{\odot}$ with $\rm Z/Z_{\odot}= 10^{-4}-10^{-6}$ illuminated by an intense Lyman Werner flux of $\rm J_{21}=10^5$. Our results show that initially the collapse proceeds isothermally with $\rm T \sim 8000$ K but dust cooling becomes effective at densities of $\rm 10^{8}-10^{12} ~cm^{-3}$ and brings the gas temperature down to a few 100-1000 K for $\rm Z/Z_{\odot} \geq 10^{-6}$. No gravitationally bound clumps are found in $\rm Z/Z_{\odot} \leq 10^{-5}$ cases by the end of our simulations in contrast to the case with $\rm Z/Z_{\odot} = 10^{-4}$. Large inflow rates of $\rm \geq 0.1~M_{\odot}/yr$ are observed for $\rm Z/Z_{\odot} \leq 10^{-5}$ similar to a zero-metallicity case while for $\rm Z/Z_{\odot} = 10^{-4}$ the inflow rate starts to decline earlier due to the dust cooling and fragmentation. For given large inflow rates a central star of $\rm \sim 10^4~M_{\odot}$ may form for $\rm Z/Z_{\odot} \leq 10^{-5}$.