SBS?0335?052W: The Lowest Metallicity Star-forming Galaxy Known

We present 4 m Kitt Peak telescope and 6.5 m MMT spectrophotometry of the extremely low metallicity galaxy SBS 0335-052W, the western companion of the blue compact dwarf galaxy SBS 0335-052E. These observations have been combined with published 10 m Keck data to derive for the brightest region of SBS 0335-052W an oxygen abundance 12 + log O/H = 7.12 ? 0.03. This makes SBS 0335-052W the lowest metallicity star-forming galaxy known in the local universe. Using a Monte Carlo technique, we fit the spectral energy distribution of SBS 0335-052W to derive the age of the oldest stars contributing to its optical light. We find that star formation in SBS 0335-052W began less than 500 Myr ago, making it a likely nearby young dwarf galaxy.