Discovery of Eight New Extremely Metal-poor Galaxies in the Sloan Digital Sky Survey

We report the discovery of eight new extremely metal-poor galaxies (XMPGs;12+log(O/H) < 7.65) and the recovery of four previously known or suspectedXMPGs (IZw18, HS0822+3542, HS0837+4717 and A1116+517) using Sloan Digital SkySurvey (SDSS) spectroscopy. These new objects were identified after an analysisof 250,000 galaxy spectra within an area of ~3000 deg^2 on the sky. Our oxygenabundance determinations have an accuracy of $\le$ 0.1 dex and are based on thetemperature-sensitive [O {\sc iii}] $\lambda$4363 \AA line and on the directcalculation of the electron temperature. We briefly discuss a new method ofoxygen abundance determinations using the [O {\sc ii}] $\lambda$7319,7330 \AA\lines, which is particularly useful for SDSS emission-line spectra withredshifts $\le$~0.024 since the [O {\sc ii}] $\lambda$3727 \AA emission linefalls outside of the SDSS wavelength range. We detect XMPGs with redshiftsranging from 0.0005 to 0.0443 and $M_g$ luminosities from $-$12\fm4 to$-$18\fm6. Our eight new XMPGs increase the number of known metal-deficientgalaxies by approximately one quarter. The estimated surface density of XMPGsis 0.004 deg$^{-2}$ for $r$ $\le$ 17\fm77.Comment: To appear in August 20 issue of ApJ Letters, 6 pages, 2 figure