Emission-Line Spectroscopy of a Damped Lyα-absorbing Galaxy at z = 0.437

Abstract

We present Keck LRIS spectra of a candidate damped Lyα (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] λ3727, Hβ, [O III] λ5007, Hα, and [N II] λ6584 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 Hα and on the reddening derived from the relative strengths of Hα and Hβ, the star formation rate is 4.7+/-0.8 M_solar yr^-1. This places the galaxy in the range of gas-rich spiral galaxies.