Observing the influence of growing black holes on the pre-reionization
  IGM
  We consider cosmological implications of the formation of first stellar size
black holes (BHs) in the universe. Such BHs form and grow by accretion in
minihaloes of masses $\simeq 10^5-10^7~M_\odot$, and emit non-thermal radiation
which impact the ionization and thermal state of the IGM. We compute the
implications of this process. We show that the influence regions for hydrogen
increase to 10kpc (physical length) for non-growing BHs to more than 0.3--1Mpc
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 $8.5<z<25$: HI 21cm line, hyperfine line of
$^3$HeII, and HI recombination lines. We show that the 21cm emitting region
around a growing BH could produce brightness temperatures $\simeq 15$mK across
an evolving structure of 1Mpc in size with hot, ionized gas closer to the BH
and much cooler in outer regions. We show that the ongoing and upcoming radio
interferometers such as LOFAR and SKA1-LOW might be able to detect these
regions. $^3$HeII emission from regions surrounding the growing BH is weak: the
corresponding brightness temperatures reaches tens of nano-Kelvin, which is
below the range of upcoming SKA1-MED. We show that for growing BHs H$\alpha$
line could be detected by JWST with $S/N=10$ in $10^4$~seconds of integration.
In light on the recent EDGES result, we show that with additional cooling of
baryons owing to collision with dark matter the HI signal could be enhanced by
more than an order of magnitude.
