Helium reionization and the thermal proximity effect
  We examine the temperature structure of the intergalactic medium IGM)
surounding a hard radiation source, such as a Quasi-Stellar Object (QSO), as it
responds to the onset of helium reionization by the source. We model the
reionization using a radiative transfer (RT) code coupled to a particle-mesh
(PM) N-body code. Neutral hydrogen and helium are initially ionized by a
starburst spectrum, which is allowed to gradually evolve into a power law
spectrum (fnu ~ nu^(-0.5)). Multiple simulations were performed with different
times for the onset and dominance of the hard spectrum, with onset redshifts
ranging from z = 3.5 to 5.5. The source is placed in a high-density region to
mimic the expected local environment of a QSO. Simulations with the source
placed in a low-density environment were also performed as control cases to
explore the role of the environment on the properties of the surrounding IGM.
We find in both cases that the IGM temperature within the HeIII region produced
exceeds the IGM temperature before full helium reionization, resulting in a
"thermal proximity effect", but that the temperature in the HeIII region
increases systematically with distance from the source. With time the
temperature relaxes with a reduced spread as a function of impact parameter
along neighbouring lines of sight, although the trend continues to persist
until z = 2. Such a trend could be detected using the widths of intervening
metal absorption systems using high resolution, high signal-to-noise ratio
spectra.
