The Concerted Impact of Galaxies and QSOs on the Ionization and Thermal
  State of the Intergalactic Medium
  We present a detailed analysis of the ionization and thermal structure of the
intergalactic medium (IGM) around a high-redshift QSO using a large suite of
cosmological, multi-frequency radiative transfer (RT) simulations, exploring
the contribution from galaxies as well as the QSO, and the effect of X-rays and
secondary ionization. We show that in high-z QSO environments both the central
QSO and the surrounding galaxies concertedly control the reionization
morphology of hydrogen and helium and have a non-linear impact on the thermal
structure of the IGM. A QSO imprints a distinctive morphology on H II regions
if its total ionizing photon budget exceeds that of the surrounding galaxies
since the onset of hydrogen reionization; otherwise, the morphology shows
little difference from that of H II regions produced only by galaxies. In
addition, the spectral shape of the collective radiation field from galaxies
and QSOs controls the thickness of the I-fronts. While a UV-obscured QSO can
broaden the I-front, the contribution from other UV sources, either galaxies or
unobscured QSO, is sufficient to maintain a sharp I-front. X-rays photons from
the QSO are responsible for a prominent extended tail of partial ionization
ahead of the I-front. QSOs leave a unique imprint on the morphology of He II /
He III regions. We suggest that, while the physical state of the IGM is
modified by QSOs, the most direct test to understand the role of galaxies and
QSOs during reionization is to perform galaxy surveys in a region of sky imaged
by 21 cm tomography.
