We present the UV spectra of two quasars obtained with the Hubble Space Telescope Advanced Camera for Surveys (HSTACS) prism (R ∼ 100). One quasar, at redshift z = 3.5, shows an absorption edge consistent either with nearly fully ionized helium with an intergalactic He II Lyα optical depth at 304 Åof τ304 > 3.1 (90% confidence), or a He m region with edge 5.4 Mpc from the QSO. The spectrum of the second quasar, at z = 3.8, has a broad absorption profile extending across the He n emission line of the quasar consistent with a damped absorption profile from an intervening He II system at z ∼ 3.7 with a column density of approximately 1022 cm -2. In this case, the extremely high He II column density and absence of strong H I absorption suggests that the radiation field is quite weak at 4 ryd. The combined He n and H I signatures are consistent with photoionization by a compact (1-100 pc) star-forming region located approximately 10 Mpc from the quasar.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science