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

Abstract

We have used STIS aboard HST to measure a sulfur abundance of [S/H] = -0.41 ± 0.06 in the ISM of the nearby DLA galaxy SBS 1543+593. A direct comparison between this QSO absorption line abundance and abundances measured from H II region emission line diagnostics yields the same result: the abundance of sulfur in the neutral 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 that have claimed order-of-magnitude differences between H I (absorption) and H II (emission) region abundances. We also derive a nickel abundance of [Ni/H] < -0.81, some 3 times less than that of sulfur, and suggest that the depletion is due to dust, although we cannot rule out an overabundance of α-elements as the cause of the lower metallicity. It is possible that our measure of [S/H] is overestimated if some S II arises in ionized gas; adopting a plausible star formation rate for the galaxy along the line of sight and a measurement of the C II* λ1335.7 absorption line detected from SBS 1543+593, we determine that the metallicity is unlikely to be smaller than 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.