Discovery of an extremely metal-poor galaxy: Optical spectroscopy of UGCA 292

The results of optical spectroscopy of two H II regions in UGCA 292 (CVn I dwA) are presented. UGCA 292 is a nearby (D = 3.1 Mpc) gas-rich dwarf irregular galaxy (M-H/L-B similar to 6.9) that was first discovered in a blind H I survey. The derived oxygen abundance is the third lowest of known star-forming galaxies [12 + log(O/H) = 7.30 +/- 0.05], making UGCA 292 one of the nearest metal-poor galaxies known. The derived N/O ratio is similar to that found in other low-metallicity galaxies [log(N/O) = -1.47 +/- 0.10] and is indicative of a primary origin for nitrogen. The derived oxygen abundance is consistent with a closed-box chemical evolution for this low-mass galaxy. The observed blue colors, high gas mass fraction, and low metallicity suggest that UGCA 292 is relatively unevolved. The possibility that future blind H I surveys may yield similar low-metallicity galaxies is discussed.