Absorption-line abundances in the smc-like galaxy ugc 5282: Evidence of ism dilution from inflows on kiloparsec Scales

We present a Hubble Space Telescope Cosmic Origins Spectrograph spectrum of the QSO SDSS J095109.12 +330745.8 (z_em= 0.645) whose sightline passes through the SMC-like dwarf galaxy UGC 5282 (M_B= -16.0, cz = 1577 km s^-1), 1.2 kpc in projection from the central H II region of the galaxy. Damped Lyα (DLA) absorption is detected at the redshift of UGC 5282 with log [N(H I) cm_-2]=20.89^+0.12 _-0.21. Analysis of the accompanying S II, PII, and O I metal lines yields a neutral gas metallicity, Z_{H I}, of [S/H] ≃ [P/H] =-0.80 ± 0.24. The metallicity of ionized gas from the central H II region Z_{H II} measured from its emission lines is [O/H] =-0.37 ± 0.10, a difference of +0.43 ± 0.26 from Z_{H I}. This difference δ is consistent with that seen toward H II regions in other star-forming galaxies and supports the idea that ionized gas near starforming regions shows systematically higher metallicities than exist in the rest of a galaxy s neutral interstellar medium (ISM). The positive values of δ found in UGC 5282 (and the other star-forming galaxies) is likely due to infalling low-metallicity gas from the intergalactic medium that mixes with the galaxy s ISM on kiloparsec scales. This model is also consistent with broad Lyα emission detected at the bottom of the DLA absorption, offset by ∼125 km s_-1 from the absorption velocity.