Isolating clusters with Wolf-Rayet stars in I Zw 18

We present UV images and spectra of the starburst galaxy I Zw 18, taken with the Space Telescope Imaging Spectrograph. The high spatial resolution of these data allows us to isolate clusters containing Wolf-Rayet stars of the subtype WC. Our far-UV spectra clearly show C IV λλ1548, 1551 and He II λ1640 emission of WC stars in two clusters: one within the bright (northwest) half of I Zw 18 and one on the outskirts of this region. The latter spectrum is unusual because the C IV is seen only in emission, indicating a spectrum dominated by WC stars. These data also demonstrate that the H I column in I Zw 18 is strongly peaked in the fainter (southeast) half of I Zw 18, with a column depth far larger than that reported in previous analyses.