An upper limit to the importance of local sources of radiation compared to the cosmic background in cosmological absorption systems is derived, as a simple consequence of the conservation of surface brightness. The limit depends only on the rate of incidence of the absorbers and the mean free path of the radiation. It is found that, on average, the ionizing radiation intensity from local source...

We describe recent discoveries of low column density (NHI ≤ 10 cm) H I Lyα absorbers made with the Hubble Space Telescope (HST) which have allowed us a first look at gas in local intergalactic space between us and the “Great Wall”. Despite the mere 2.4m aperture of HST, these new observations allow us to detect absorbers with column densities, NHI ≈ 10 12.5 cm, as low as those found using Keck/...

We have conducted a systematic survey for intervening OVI absorbers in available echelle spectra of 16 QSOs at zQSO = 0.17 − 0.57. These spectra were obtained using HST/STIS with the E140M grating. Our search uncovered a total of 27 foreground O VI absorbers with rest-frame absorption equivalent width Wr(1031) & 25 mÅ. Ten of these QSOs exhibit strong OVI absorbers in their vicinity. Our OVI su...