Ionizing Radiation Fluctuations and Large‐Scale Structure in the Lyα Forest

We investigate the large-scale inhomogeneities of the hydrogen ionizing radiation field in the Universe at redshift z=3. Using a raytracing algorithm, we simulate a model in which quasars are the dominant sources of radiation. We make use of large scale N-body simulations of a LambdaCDM universe, and include such effects as finite quasar lifetimes and output on the lightcone, which affects the shape of quasar light echoes. We create Lya forest spectra that would be generated in the presence of such a fluctuating radiation field, finding that the power spectrum of the Lya forest can be suppressed by as much as 15 % for modes with k=0. 05-1 Mpc/h. This relatively small effect may have consequences for high precision measurements of the Lya power spectrum on larger scales than have yet been published. We also investigate another radiation field probe, the cross-correlation of quasar positions and the Lya forest. For both quasar lifetimes which we simulate (10⁷ yr and 10⁸ yr), we expect to see a strong decrease in the Lya absorption close to other quasars (the ``foreground'' proximity effect). We then use data from the Sloan Digital Sky Survey First Data Release to make an observational determination of this statistic. We find no sign of our predicted lack of absorption, but instead increased absorption close to quasars. If the bursts of radiation from quasars last on average 10⁴yr and < 10⁶ yr could reconcile these two facts.