IMPACT OF DUST COOLING ON DIRECT-COLLAPSE BLACK HOLE FORMATION

Observations of quasars at z\gt 6 suggest the presence of black holes with a few times {10}9\quad {M}⊙ . Numerous models have been proposed to explain their existence, including a direct collapse, which provides massive seeds of {10}5\quad {M}⊙ . The isothermal direct collapse requires a strong Lyman-Werner (LW) flux to quench {{{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 \gt {10}7\quad {M}⊙ with Z/{Z}⊙ ={10}-4{--}{10}-6 illuminated by an intense LW flux of {J}21={10}5. Our results show that initially the collapse proceeds isothermally with T∼ 8000 K, but dust cooling becomes effective at densities of {10}8{--}{10}12 {{cm}}-3 and brings the gas temperature down to a few 100-1000 K for Z/{Z}⊙ ≥slant {10}-6. No gravitationally bound clumps are found in the Z/{Z}⊙ ≤slant {10}-5 cases by the end of our simulations, in contrast to the case with Z/{Z}⊙ ={10}-4. Large inflow rates of ≥slant 0.1\quad {M}⊙ {{yr}}-1 are observed for Z/{Z}⊙ ≤slant {10}-5, similar to a zero-metallicity case, while for Z/{Z}⊙ ={10}-4 the inflow rate starts to decline earlier because of dust cooling and fragmentation. For given large inflow rates, a central star of ∼ {10}4\quad {M}⊙ may form for Z/{Z}⊙ ≤slant {10}-5.