A New Extremely Low-Metallicity Galaxy Discovered in the SDSS

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The SDSS spectroscopic database, which will ultimately contain spectra of one million galaxies, provides an ideal resource for searches for extremely low-metallicity galaxies. Using the current version of the database we studied 135,000 galaxy spectra to calculate the oxygen abundance. We used only spectra in which the [OIII] 4363 Å line was detected. Among this vast number of galaxies, we discovered only one new extremely metal-poor galaxy: SDSS J0519+0007. It has an oxygen abundance of only 12+log(O/H) = 7.45 +/- 0.02 or 1/30 of our Sun. This makes it the sixth galaxy in the short list of very metal-poor galaxies, and the first one discovered with SDSS data. We derived abundances of O, Ne, Ar, N, S, and He for SDSS J0519+0007. Abundance ratios for α -elements for this galaxy are in good agreement with the mean values for other very metal-deficient blue compact galaxies (except for nitrogen). The broad low-contrast component in the Hα emission line indicates the presence of fast motions in this galaxy. We also detect the characteristic blue bump, a signature of Wolf-Rayet stars, in the SDSS spectrum. SDSS J0519+0007 is a new low-metallicity dwarf galaxy with a luminosity of MB ~ -18 mag (redshift 0.044). This is more than 3 mag brighter than any previously known galaxy of such low metallicity and indicates that such objects may span a total range of luminosities of more than 6 magnitudes.

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