METAL ENRICHMENT, DUST, AND STAR FORMATION IN GALAXIES AT HIGH REDSHIFTS .2. LYMAN-ALPHA EMISSION FROM THE Z = 2.465 ABSORBER TOWARD Q0836+113

QSO absorption systems with damped Lya lines have been suggested as the high-redshift progenitors of present-day galaxies. As part of a survey of element abundances and star formation rates in these systems, we have obtained long-slit, 1.5 Å resolution spectroscopic observations of the zcm = 2.67 QSO 0836+113. We report the detection of a narrow emission line (at a 4.0-4.5 σ level), centered in the black core of the damped Lya absorption line at zabs = 2.465, which we interpret as Lyα from star-forming H II regions associated with the z = 2.465 galaxy. This is the first detection of Lyα emission from a galaxy identified by its absorption signature. The narrow velocity width of the emission line (FWHM < 60 km s-1), its small spatial extent (<9 times; 17 kpc), and its close alignment with the QSO sightline argue in favor of this damped system arising in a gas-rich H II galaxy. The inferred star formation rate, derived from the observed Lyα luminosity, is ∼ 1 M⊙ yr-1. This is directly comparable with rates measured for nearby H II galaxies and consistent with limits for damped Lyα systems set by other workers. We discuss the implications of the detection on future observational studies, emphasizing the need for low detector noise and high signal-to-noise ratio (S/N) for the sky background. In this particular case, the emission region is probably confined within 1″ of the sightline to the QSO, making it very difficult to achieve a detection by narrow-band imaging.