The High-Redshift He II Gunn-Peterson Effect: Implications and Future Prospects

摘要: Absorption due to He II Lyα has now been detected at low resolution in the spectra of four quasars between redshifts z = 2.74 and 3.29. We assess these observations, giving particular attention radiative transfer ionizing background radiation, cloud diffuse emission ionization physics, statistical fluctuations. use high-resolution observations H I absorption toward derive an improved model for opacity intergalactic medium (IGM) from distribution absorbing clouds column density redshift. models calculate photoionization history, ratio η II/H both optically thin self-shielded clouds, average line-blanketing contribution absorption. The derived rate, ΓH (1–3) × 10-12 s-1 (z 2–4), is consistent with intensity inferred "proximity effect," but it remains larger than that by N-body hydrodynamic simulations absorber distribution. are line blanketing having NH ≥ 1012 cm-2, although a more IGM would help explain observed opacity. compute expected optical depth, τHe I(z), examine implications sizable fluctuations arise variations numbers radiation field. how constrains spectrum fractional contributions dominant sources (quasars starburst galaxies). Finally, we demonstrate ultraviolet can distinguish forest determine source background.