Infrared background signatures of the first black holes

Understand

Angular fluctuations of the Near InfraRed Background (NIRB) intensity are observed up to scales $\simlt 1^{\ensuremath{^{\circ}}}$.

• Their interpretation is challenging as even after removing the contribution from detected sources, the residual signal is $>10$ times higher than expected from distant galaxies below the detection limit and first stars.
• We propose here a novel interpretation in which early, intermediate mass, accreting direct collapse black holes (DCBH), which are too faint to be detected individually in current surveys, could explain the observed fluctuations.
• We find that a population of highly obscured ($N_{\rm H}\simgt 10^{25} \rm cm^{-2}$) DCBHs formed in metal-free halos with virial temperature $10^4$ K at $z\simgt 12$, can explain the observed level $\approx 10^{-3}$ (nW m$^{-2}$ sr$^{-1})^2$ of the 3.6 and 4.5 $\mu$m fluctuations on scales $>100''$.