Impact of dust cooling on direct collapse black hole formation
  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 $\rm Z/Z_{\odot} \leq
10^{-5}$.
