Lyalpha versus X-ray heating in the high-z IGM
  In this paper we examine the effect of X-ray and Lyalpha photons on the
intergalactic medium temperature. We calculate the photon production from a
population of stars and micro-quasars in a set of cosmological hydrodynamic
simulations which self-consistently follow the dark matter dynamics, radiative
processes as well as star formation, black hole growth and associated feedback
processes. We find that, (i) IGM heating is always dominated by X-rays unless
the Lyalpha photon contribution from stars in objects with mass M<10^8 Msun
becomes significantly enhanced with respect to the X-ray contribution from BHs
in the same halo (which we do not directly model). (ii) Without overproducing
the unresolved X-ray background, the gas temperature becomes larger than the
CMB temperature, and thus an associated 21 cm signal should be expected in
emission, at z<11.5. We discuss how in such a scenario the transition redshift
between a 21 cm signal in absorption and in emission could be used to
constraint BHs accretion and associated feedback processes.
