Revisiting the He ii to H i ratio in the intergalactic medium

摘要: We estimate the He II to HI column density ratio, η = N(He II)/N(He I), in intergalactic medium towards high-redshift (z em 2.885) bright quasar QSO HE 2347-4342 using Voigt-profile fitting of H I transitions Lyman series and α transition as observed by FUSE satellite. In agreement with previous studies, we find that > 50 most forest, except four regions where it is much smaller (η ~ 10-20) therefore inconsistent photoionization ultraviolet background flux. detect O VI CIV absorption lines associated two these abs 2.6346 2.6498). show that, if constrain fit and/or profiles presence metal components, can accommodate values range 15-100 systems, assuming broadening intermediate between pure thermal turbulent. While simple models reproduce N(O VI)/N(C iv) they fail produce low values, contrast high temperatures (i.e T ≥ 10 5 K). The Doppler parameters measured for different species suggest a multiphase nature absorbing regions. Therefore, were be confirmed, would favour model which gas at temperature (> K) but metals, particular C IV, are due lower-temperature (~few 4 photoionized gas.