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

Abstract

We report new imaging and spectroscopic observations of the dampedLy? absorber (DLA) galaxy SBS 1543+593, a nearby dwarf galaxy whosestellar disk is intersected by the sight line to the bright backgroundQSO HS 1543+5921. Hubble Space Telescope imaging observations withWFPC2 in the F450W and F702W bands are used to measure the DLA galaxy'sproperties and compile a catalog of its (candidate) H II regions.Ground-based long-slit spectroscopy of the brightest H II regionin the galaxy yields estimates of the star formation rate (SFR) andchemical abundances in the galaxy's interstellar medium. We findthat SBS 1543+593 exhibits an SFR of ~0.006h-270 Msolar yr-1, oran SFR per unit area of ~1.4�10-4h-270 Msolar yr-1 kpc-2. We derivegas-phase abundances in the ionized gas of 12+log(O/H)=8.2+/-0.2,which is about 1/3 of the solar value, and log(N/O)=-1.40+0.2-0.3.These values are consistent with the morphological appearance ofSBS 1543+593, an Sm dwarf of MB-5logh70=-16.8+/-0.2 and intermediatesurface brightness. SBS 1543+593 is the first bona fide DLA for whichabundances have been measured using emission-line diagnostics. Whencompared with future high-resolution ultraviolet spectroscopy, ourresults should prove key for interpreting abundance determinationsin high-redshift DLAs.