Emission Line Spectroscopy of a Damped Lyman-alpha Absorbing Galaxy at z = 0.437
Abstract
We present Keck/LRIS spectra of a candidate damped Lyman-alpha (DLA) galaxy toward the QSO 3C196 (zem = 0.871). The DLA absorption system has a redshift of zDLA = 0.437, and a galaxy at 1.5" from the QSO has been identified in high resolution imaging with WFPC2/HST. We have detected emission lines of [O II] 3727A, Hbeta, [O III] 5007A, Halpha and [N II] 6584A at the absorption redshift. Based on the emission lines, we have found the redshift of the galaxy to be zem = 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 ISM of the DLA galaxy has a high metallicity comparable to or perhaps twice as much as solar (e.g. 12+log (O/H) = 8.98 +/- 0.07). Based on the strengths of Halpha and on the reddening derived from the relative strengths of Halpha and Hbeta, the star formation rate is 4.7 +/- 0.8 Msolar/yr. This places the galaxy in the range of gas-rich spiral galaxies.
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