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

Abstract

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 ~0.006h^-2₇₀ M_solar yr^-1, or an SFR per unit area of ~1.4×10^-4h^-2₇₀ M_solar 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 1/3 of the solar value, and log(N/O)=-1.40^+0.2_-0.3. These values are consistent with the morphological appearance of SBS 1543+593, an Sm dwarf of M_B-5logh₇₀=-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.

Based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.