A Comparison of Absorption‐ and Emission‐Line Abundances in the Nearby Damped Lyα Galaxy SBS 1543+593

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Abstract
We have used the Space Telescope Imaging Spectrograph (STIS) aboard HST to measure a sulfur abundance of (S/H) = -0.41 ± 0.06 in the interstellar medium (ISM) of the nearby damped Lyman-� (DLA) absorbing galaxy SBS 1543+593. A direct comparison between this QSO absorption line abundance on the one hand, and abundances measured from H II region emission line diagnostics on the other, yield the same result: the abundance of sulfur in the neu- tral ISM is in good agreement with that of oxygen measured in an H II region 3 kpc away. Our result contrasts with those of other recent studies which have claimed order-of-magnitude differ- ences between H I (absorption) and H II (emission) region abundances. We also derive a nickel abundance of (Ni/H) < -0.81, some three times less than that of sulfur, and suggest that the de- pletion is due to dust, although we cannot rule out an over-abundance of alpha-elements as the cause of the lower metallicity. It is possible that our measu re of (S/H) is over-estimated if some S II arises in ionized gas; adopting a plausible star formati on rate for the galaxy along the line of sight, and a measurement of the C II∗ �1335.7 absorption line detected from SBS 1543+593, we determine that the metallicity is unlikely to be smaller tha n we derive by more than 0.25 dex. We estimate that the cooling rate of the cool neutral medium is log (lc (ergs s-1 H atom-1)) ≈ -27.0, the same value as that seen in the high redshift DLA population.
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