[Previous] | [Session 3] | [Next]
R.C. Telfer, W. Zheng, A.F. Davidsen (Johns Hopkins University), G.A. Kriss (Space Telescope Science Institute)
Using archival HST FOS and GHRS data, we generate composite QSO spectra of many intervening Lyman forest absorbers at z ~2 to search for associated metal lines in the far UV. This technique has been applied previously at longer wavelengths, with particular emphasis on C~IV \lambda\lambda1548, 1551, but no thorough search for metal lines below ~900 Å\ has been reported. Including 39 intervening absorption systems along two sight lines with rest-frame Ly\alpha equivalent widths > 0.4 Å, where known Lyman-limit systems are excluded, we find an O~V \lambda630 feature in the median combined spectrum with a rest-frame equivalent width of 110±40 mÅ, corresponding to a column density NOV = 1013.8{\rm cm -2} if the absorption is unsaturated. Simulated composite spectra using randomly chosen absorber redshifts indicate that the detection is real with > 99% confidence. We estimate the median H~I column density of the sample to be 1014.8 {\rm cm -2}, implying log(OV / HI) ~-1, more than a factor of two larger than current models suggest. In the context of physical models, these data can be used along with previous studies of metals in the Lyman forest to constrain the ionization state and chemical composition of the intergalactic medium.