We present an HST Cosmic Origins Spectrograph ( COS ) 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 \ion H2 region of the galaxy .
Damped Ly \alpha ( DLA ) absorption is detected at the redshift of UGC 5282 with \log [ N ( \ion H1 ) cm ^ { -2 } ] = 20.89 ^ { +0.12 } _ { -0.21 } .
Analysis of the accompanying \ion S2 , \ion P2 and \ion O1 metal lines yields a neutral gas metallicity , Z _ { \text { H~ { } I } } , of [ S/H ] \ > \simeq \ > [ P/H ] \ > = -0.80 \pm 0.24 .
The metallicity of ionized gas from the central \ion H2 region , Z _ { \text { H~ { } II } } , measured from its emission lines is [ O/H ] = -0.37 \pm 0.10 , a difference of +0.43 \pm 0.26 from Z _ { \text { H~ { } I } } .
This difference \delta is consistent with that seen towards \ion H2 regions in other star-forming galaxies and supports the idea that ionized gas near star forming regions shows systematically higher metallicities than exist in the rest of a galaxy ’ s neutral interstellar medium ( ISM ) .
The positive values of \delta 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 kpc scales .
This model is also consistent with broad Ly \alpha emission detected at the bottom of the DLA absorption , offset by \sim 125 km s ^ { -1 } from the absorption velocity .
Models of galaxy evolution that attempt to replicate population characteristics , such as the mass-metallicity relation , may need to start with a galaxy metallicity represented by Z _ { \text { H~ { } I } } rather than that measured traditionally from Z _ { \text { H~ { } II } } .