The Evolution of the Ultraviolet Background

摘要: Knowledge of photoionization rates in intergalactic gas is important for modeling the growth structure and formation galaxies. We present measurements these using proximity effect a sample over 200 ground-based HST/FOS quasar spectra covering 0.03 < z 3.8. These confirm evolution ultraviolet background (UVB) from ∼ 2 to that expected due decline space density. The measured HI ionization rate factor ∼10 lower at 0.5 than – 3. integrated UV emission quasars can account observed UVB ≲ 4 given measurement uncertainties. simulated Lyα forest created log-normal approximation linear mildly non-linear density velocity fields. effects placed fields on surrounding medium (IGM) are incorporated into synthetic spectra. find maximum likelihood methods reliably estimate metagalactic if do not preferentially occupy regions significant overdensity, clustering mass around will bias ΓHI upward by ∼3.