The Lyman-alpha emission-line profiles in high-redshift QSOs

Abstract

High-resolution (~ 1 Å) spectra of six high-redshift QSOs were utilized in a study of the profile of the Lyα λ 1215.67 Å emission line. The symmetry of the prof:tle was studied after removing any absorption lines, which are mostly resolved at this resolution and after subtraction of N V λ1240 and Si II λ1263 emission from the observed blend. With one exception, Q2204 – 408, the Lyα profiles are symmetric to within the uncertainties of the procedure. It also became clear during the analysis that the profiles of the emission lines are not identical, in particular C IV λ 1549 generally has weaker wings and peak than Lyα λ 1216. It is argued that either the motion of the broad-line region gas is not purely radial, or else most of the Lyα photons originate in optically-thin gas. Further implications of these results are discussed.