Sbs 0335–052w: the Lowest-metallicity Star-forming Galaxy Known

We present 4-meter Kitt Peak telescope and 6.5-meter 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-meter 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. Subject headings: galaxies: abundances — galaxies: irregular — galaxies: evolution — galaxies: formation — galaxies: ISM — H ii regions — ISM: abundances