Observing the Influence of Growing Black Holes on the Pre-reionization IGM

Abstract

We consider the cosmological implications of the formation of the first stellar size black holes (BHs) in the universe. Such BHs form and grow by accretion in minihaloes of masses sime105–107 ${M}_{\odot }$, and emit nonthermal radiation that affects the ionization and thermal state of the intergalactic medium (IGM). We compute the implications of this process. We show that the influence regions for hydrogen increase to 10 kpc (physical length) for non-growing BHs to more than 0.3–1 Mpc for accreting BHs; the influence regions are ten times smaller for singly ionized helium. We consider three possible observables from the influence zones around accreting BHs during 8.5 < z < 25: the H i 21 cm line, the hyperfine line of 3He ii, and the H i recombination lines. We show that the 21 cm emitting region around a growing BH could produce brightness temperatures sime15 mK across an evolving structure of 1 Mpc with hot, ionized gas closer to the BH and much cooler gas in outer regions. We show that current and upcoming radio interferometers such as the Low Frequency Array (LOFAR) and the Square Kilometre Array (SKA) SKA1-LOW might be able to detect these regions. The 3He ii emission from regions surrounding the growing BH is weak: the corresponding brightness temperatures reach tens of nano-Kelvin, which is below the range of the upcoming SKA1-MED. We show that for growing BHs, the Hα line could be detected by the James Webb Space Telescope with a signal-to-noise ratio of 10 in 104 s of integration. In light on the recent result of the Experiment to Detect the Global EoR Signature (EDGES), we show that with additional cooling of baryons owing to collision with dark matter, the H i signal could be enhanced by more than an order of magnitude.