Possible Detection of Lyα Fluorescence from a Damped Lyα System at Redshift z ~ 2.8

We have detected Lyα emission from a damped Lyα system (DLA) that lies near the bright quasar HS1549+1919. The DLA has the same redshift as HS1549+1919 and was discovered in the spectrum of a faint QSO that lies 49" away (380 proper kpc). The emission line's luminosity, double-peaked profile, and small spatial separation from the DLA suggest that it may be fluorescent Lyα emission from gas that is absorbing the nearby QSO's radiation. If this is the case, our observations show that the DLA has a size of at least 1.5" and that the QSO's luminosity 1 million years ago was similar to its luminosity today. A survey for similar systems within ~1' of bright QSOs would put interesting limits on the mean quasar lifetime.

Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership between the California Institute of Technology, the University of California, and NASA, and made possible by the generous financial support of the W. M. Keck Foundation.