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

We have used the Space Telescope Imaging Spectrograph (STIS) aboard HST tomeasure a sulfur abundance of [S/H] = -0.41 +/-0.06 in the interstellar medium(ISM) of the nearby damped Lyman-alpha (DLA) absorbing galaxy SBS 1543+593. Adirect comparison between this QSO absorption line abundance on the one hand,and abundances measured from HII region emission line diagnostics on the other,yield the same result: the abundance of sulfur in the neutral ISM is in goodagreement with that of oxygen measured in an HII region 3 kpc away. Our resultcontrasts with those of other recent studies which have claimedorder-of-magnitude differences between HI (absorption) and HII (emission)region abundances. We also derive a nickel abundance of [Ni/H] < -0.81, somethree times less than that of sulfur, and suggest that the depletion is due todust, although we cannot rule out an over-abundance of alpha-elements as thecause of the lower metallicity. It is possible that our measure of [S/H] isover-estimated if some SII arises in ionized gas; adopting a plausible starformation rate for the galaxy along the line of sight, and a measurement of theCII* 1335.7 absorption line detected from SBS 1543+593, we determine that themetallicity is unlikely to be smaller than we derive by more than 0.25 dex. Weestimate that the cooling rate of the cool neutral medium is log [l_c (ergss^{-1} H atom^{-1})] = -27.0, the same value as that seen in the high redshiftDLA population.Comment: 31 pages; accepted for publication in the Ap