Emission-line spectroscopy of a damped Lyα-absorbing galaxy at z=0.437

We present Keck LRIS spectra of a candidate damped Ly alpha (DLA) galaxy toward the QSO 3C 196 (z(em) 0.871). The DLA absorption system has a redshift of z(DLA) = 0.437, and a galaxy at 1.5 '' from the QSO has been identified in high-resolution imaging with WFPC2 on board the Hubble Space Telescope. We have detected emission lines of [O II] lambda 3727, H beta, [O III] lambda 5007, H alpha, and [N II] lambda 6584 at the absorption redshift. Based on the emission lines, we have found the redshift of the galaxy to be z(em) 0.4376 +/- 0.0006. The emission lines also enabled us to calculate the extinction-corrected luminosities and metallicity indicators using established indices based on line strengths of different emission lines. These indicators suggest that the interstellar medium of the DLA galaxy has a high metallicity comparable to or perhaps twice as much as solar [i.e., 12 + log (O/H) = 8.98 +/- 0.07]. Based on the strengths of H alpha and on the reddening derived from the relative strengths of H alpha and H alpha, the star formation rate is 4.7 +/- 0.8 M-circle dot yr(-1). This places the galaxy in the range of gas-rich spiral galaxies.