The location of material producing Lyman-limit discontinuities in QSO spectra

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Abstract
We have studied a sample of QSOs having continuum absorption breaks near 912 Å in the emission-line rest frame. Of eight QSOs which are sufficiently well observed to comment on the location of the absorbing material, seven almost certainly have the absorbing material somewhere out-side the emission-line region. The other case, though ambiguous, is also consistent with absorption by material external to the QSO. By including data from other samples, we conclude that the covering factor ∊ for large clouds of emitting material is less than 0.09 and that the data are entirely consistent with ∊ < 0.02. The small observed values of the Lyα/Hβ intensity ratio for QSO emission lines are therefore unlikely to arise from selective Lyα depletion. Three of the five quasars which we observed at Cerro Tololo showed broad absorption features in their spectra. In one object we discovered a huge trough of N V absorption which might be spread over a range of ejection velocity as large as 54 000 km s−1 (0.18c).

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