The UV Spectrum of the QSO OQ 172 Observed with the Faint Object Spectrograph
Cohen, Ross D.; Junkkarinen, Vesa T.; Lyons, R. W.; Burbidge, E. Margaret; Beaver, E. A.
Abstract
Low resolution far-UV spectra of the high redshift QSO OQ 172 (Z_e_ = 3.544) have been obtained with the prism and the G160L grating of the Faint Object Spectrograph on board the Hubble Space Telescope. Light is detected down to a rest wavelength near 325 A where the spectrum appears to be cut off, possibly by a Lyman limit system. This cutoff is about 20,000 km s^-1^ longward of any predicted He II λ304 feature (the He II λ304 Gunn-Peterson effect and the He II λ304 forest). A partial Lyman limit is observed near 2826 A (z =2. 10). The UV spectra have been combined with optical CCD spectra to determine the shape of the continuum short of the Lyα emission line and model it using the "Lyman valley" equations presented by Miller & Jakobsen (A&A, 228,299(1990)].