SIMBAD references

We present 8.2m VLT spectroscopic observations of 28 HII regions in 16 emission-line galaxies and 3.6m ESO telescope spectroscopic observations of 38 HII regions in 28 emission-line galaxies. These emission-line galaxies were selected mainly from the data release 6 (DR6) of the Sloan digital sky survey (SDSS) as metal-deficient galaxy candidates. We collect photometric and high-quality spectroscopic data for a large uniform sample of star forming galaxies including new observations. Our aim is to study the luminosity-metallicity (L-Z) relation for nearby galaxies, especially at its low-metallicity end and compare it with that for higher-redshift galaxies. Physical conditions and element abundances in the new sample are derived with the T_e-method, excluding six HII regions from the VLT observations and nearly two third of the HII regions from the 3.6m observations. Element abundances for the latter galaxies were derived with the semiempirical strong-line method. From our new observations we find that the oxygen abundance in 61 out of the 66 HII regions of our sample ranges from 12+logO/H=7.05 to 8.22. Our sample includes 27 new galaxies with 12+logO/H<7.6 which qualify as extremely metal-poor star-forming galaxies (XBCDs). Among them are 10 HII regions with 12+logO/H<7.3. The new sample is combined with a further 93 low-metallicity galaxies with accurate oxygen abundance determinations from our previous studies, yielding in total a high-quality spectroscopic data set of 154 HII regions. 9000 more galaxies with oxygen abundances, based mainly on the T_e-method, are compiled from the SDSS. Photometric data for all galaxies of our combined sample are taken from the SDSS database while distances are from the NED. Our data set spans a range of 8mag with respect to its absolute magnitude in SDSS g (-12>M_g>-20) and nearly 2dex in its oxygen abundance (7.0≲12+logO/H≲8.8), allowing us to probe the L-Z relation in the nearby universe down to the lowest currently studied metallicity level. The L-Z relation established on the basis of the present sample is consistent with previous ones obtained for emission-line galaxies.