The Epoch of IGM heating by early sources of X-rays
  Observations of the 21 cm line from neutral hydrogen indicate that an Epoch
of Heating (EoH) might have preceded the later Epoch of Reionization (EoR).
Here we study the effects on the ionization state and the thermal history of
the Intergalactic Medium (IGM) during the EoH induced by different assumptions
on ionizing sources in the high redshift Universe: (i) stars, (ii) X-ray
binaries (XRBs), (iii) thermal bremsstrahlung of the hot Interstellar Medium
(ISM), and (iv) accreting nuclear black holes (BHs). To this aim, we
post-process outputs from the ($100 h^{-1}$ cMpc)$^3$ hydrodynamical simulation
MassiveBlack-II with the cosmological 3D radiative transfer code CRASH, which
follows the propagation of UV and X-ray photons, computing the thermal and
ionization state of hydrogen and helium through the EoH. We find that stars
determine the fully ionized morphology of the IGM, while the spectrally hard
XRBs pave way for efficient subsequent heating and ionization by the spectrally
softer ISM. With the seeding prescription in MassiveBlack-II, BHs do not
contribute significantly to either ionization or heating. With only stars, most
of the IGM remains in a cold state (with a median $T=11$ K at $z=10$), however,
the presence of more energetic sources raises the temperature of regions around
the brightest and more clustered sources above that of the CMB, opening the
possibility to observing the 21 cm signal in emission.
