The HII Regions of the Damped Lyman alpha Absorber SBS 1543+593

摘要

We report new imaging and spectroscopic observations of the damped Ly alpha(DLA) galaxy SBS 1543+593, a nearby dwarf galaxy whose stellar disk isintersected by the sightline to the bright background QSO HS 1543+5921. HubbleSpace Telescope imaging observations with WFPC2 in the F450W and F702W bandsare used to measure the DLA galaxy's properties and compile a catalog of its(candidate) HII regions. Ground-based long-slit spectroscopy of the brightestHII region in the galaxy yields estimates of the star formation rate (SFR) andof chemical abundances in the galaxy's interstellar medium. We find that SBS1543+593 exhibits a SFR $pprox 0.006 h^{-2}_{70} M_{odot}$ yr$^{-1}$, or aSFR per unit area of $pprox 1.4 imes 10^{-4} h^{-2}_{70} M_odot$ yr$^{-1}$kpc$^{-2}$. We derive gas-phase abundances in the ionized gas of $12 + log{m (O/H)} = 8.2 pm 0.2$, which is about 1/3 of the solar value, and $log{m (N/O)} = -1.40^{+0.2}_{-0.3}$. These values are consistent with themorphologial appearance of SBS 1543+593, an Sm dwarf of $M_B -5 log h_{70} =-16.8pm0.2$ and of intermediate surface brightness. SBS 1543+593 is the first{it bona fide} DLA for which abundances have been measured using emission-linediagnostics. When compared with future, high-resolution, ultravioletspectroscopy, our results should prove key for interpreting abundancedeterminations in high redshift DLAs.