Semi-numeric simulations of helium reionization and the fluctuating
  radiation background
  Recent He II Lyman-alpha forest observations from 2.0 < z < 3.2 show large
fluctuations in the optical depth at z > 2.7. These results point to a
fluctuating He-ionizing background, which may be due to the end of helium
reionization of this era. We present a fast, semi-numeric procedure to
approximate detailed cosmological simulations. We compute the distribution of
dark matter halos, ionization state of helium, and density field at z = 3 in
broad agreement with recent simulations. Given our speed and flexibility, we
investigate a range of ionizing source and active quasar prescriptions.
Spanning a large area of parameter space, we find order-of-magnitude
fluctuations in the He II ionization rate in the post-reionization regime.
During reionization, the fluctuations are even stronger and develop a bimodal
distribution, in contrast to semi-analytic models and the hydrogen equivalent.
These distributions indicate a low-level ionizing background even at
significant He II fractions.
