Cosmological radiative transfer for the line-of-sight proximity effect
  We study the proximity effect in the Ly-a forest around high redshift quasars
as a function of redshift and environment employing a set of 3D radiative
transfer simulations.
  The analysis is based on dark matter only simulations at redshifts 3, 4, and
4.9 and, adopting an effective equation of state for the baryonic matter, we
infer the HI densities and temperatures in the cosmological box. The UV
background (UVB) and additional QSO radiation with Lyman limit flux of L_{\nu
LL} = 1e31 and 1e32 erg / Hz s are implemented with a radiative transfer code
until an equilibrium configuration is reached. We analyse mock spectra
originating at the QSO in the most massive halo, in a random filament and in a
void. The proximity effect is studied using flux transmission statistics, in
particular with the normalised optical depth.
  Beyond a radius of r > 1 Mpc / h from the quasar, we measure a transmission
profile consistent with geometric dilution of the QSO ionising radiation. A
departure from geometric dilution is only seen, when strong absorbers intervene
the line-of-sight. The cosmic density distribution around the QSO causes a
large scatter in the normalised optical depth. The scatter decreases with
increasing redshift and increasing QSO luminosity. The mean proximity effect
provides an average signal that is biased by random large scale density
enhancements on scales up to r \approx 15 Mpc / h. The distribution of the
proximity effect strength provides a measure of the proximity effect along
individual lines of sight. It shows a clear maximum almost without an
environmental bias. Therefore it can be used for an unbiased estimate of the
UVB. Differing spectral energy distributions between the QSO and the UVB modify
the profile which can be reasonably well corrected analytically. A few Lyman
limit systems have been identified that prevent the detection of the proximity
effect due to shadowing.
