The H II Regions of the Damped Lyα Absorber SBS 1543+593

We report new imaging and spectroscopic observations of the damped Lyα absorber (DLA) galaxy SBS 1543+593, a nearby dwarf galaxy whose stellar disk is intersected by the sight line to the bright background QSO HS 1543+5921. Hubble Space Telescope imaging observations with WFPC2 in the F450W and F702W bands are used to measure the DLA galaxy's properties and compile a catalog of its (candidate) H II regions. Ground-based long-slit spectroscopy of the brightest H II region in the galaxy yields estimates of the star formation rate (SFR) and chemical abundances in the galaxy's interstellar medium. We find that SBS 1543+593 exhibits an SFR of ≈0.006 h M☉ yr-1, or an SFR per unit area of ≈1.4 × 10-4 h M☉ yr-1 kpc-2. We derive gas-phase abundances in the ionized gas of 12 + log (O/H) = 8.2 ± 0.2, which is about of the solar value, and log (N/O) = -1.40. These values are consistent with the morphological appearance of SBS 1543+593, an Sm dwarf of MB - 5 log h70 = -16.8 ± 0.2 and intermediate surface brightness. SBS 1543+593 is the first bona fide DLA for which abundances have been measured using emission-line diagnostics. When compared with future high-resolution ultraviolet spectroscopy, our results should prove key for interpreting abundance determinations in high-redshift DLAs.