It has been proposed that the first , intermediate-mass ( \approx 10 ^ { 5 - 6 } ~ { } M _ { \odot } ) black holes might form through direct collapse of unpolluted gas in atomic-cooling halos exposed to a strong Lyman-Werner ( LW ) or near-infrared ( NIR ) radiation .
As these systems are expected to be Compton-thick , photons above 13.6 eV are largely absorbed and re-processed into lower energy bands .
It follows that direct collapse black holes ( DCBHs ) are very bright in the LW/NIR bands , typically outshining small high-redshift galaxies by more than 10 times .
Once the first DCBHs form , they then trigger a runaway process of further DCBH formation , producing a sudden rise in their cosmic mass density .
The universe enters the “ DCBH era ” at z \approx 20 when a large fraction of atomic-cooling halos are experiencing DCBH formation .
By combining the clustering properties of the radiation sources with Monte Carlo simulations we show that in this scenario the DCBH mass density rises from \sim 5 M _ { \odot } Mpc ^ { -3 } at z \sim 30 to the peak value \sim 5 \times 10 ^ { 5 } M _ { \odot } Mpc ^ { -3 } at z \sim 14 in our fiducial model .
However , the abundance of active ( accreting ) DCBHs drops after z \sim 14 , as gas in the potential formation sites ( unpolluted halos with virial temperature slightly above 10 ^ { 4 } K ) is photoevaporated .
This effect almost completely suppresses DCBH formation after z \sim 13 .
The DCBH formation era lasts only \approx 150 Myr , but it might crucially provide the seeds of the supermassive black holes ( SMBHs ) powering z \sim 6 quasars .