Measurement of [O III] emission in Lyman-break galaxies

Measurements of [O III] emission in Lyman-break galaxies (LBGs) at z > 3 ar e presented. Four galaxies were observed with narrowband filters using the near-IR camera on the Keck I 10 m telescope. A fifth galaxy was observed sp ectroscopically during the commissioning of NIRSPEC, the new infrared spect rometer on Keck II. The emission-line spectrum is used to place limits on t he metallicity. Comparing these new measurements with others available from the literature, we find that strong oxygen emission in LBGs may suggest su bsolar metallicity for these objects. The [O III] lambda 5007 line is also used to estimate the star formation rate (SFR) of the LBGs. The inferred SF Rs are higher than those estimated from the UV continuum, and may be eviden ce for dust extinction.