Metal Abundances of KISS Galaxies. I. Coarse Metal Abundances and the Metallicity-Luminosity Relation

We derive metal abundance estimates for a large sample of starburstingemission-line galaxies (ELGs). Our sample is drawn from the KPNO InternationalSpectroscopic Survey (KISS) which has discovered over 2000 ELG candidates todate. Follow-up optical spectra have been obtained for ~900 of these objects. Athree step process is used to obtain metal abundances for these galaxies. Wefirst calculate accurate nebular abundances for 12 galaxies whose spectra coverthe full optical region from [OII]3726,29 to beyond [SII]6717,31 and includedetection of [OIII]4363. Using secondary metallicity indicators R_23 and p_3,we calculate metallicities for an additional 59 galaxies with spectra thatcover a similar wavelength range but lack [OIII]4363. The results are used tocalibrate relations between metallicity and two readily observed emission-lineratios, which allow us to estimate coarse metallicities for 519 galaxies intotal. The uncertainty in these latter abundance estimates is 0.16 dex. Fromthe large, homogeneously observed sample of star-forming galaxies we identifylow metallicity candidates for future study and investigate themetallicity-luminosity relation. We find a linear metallicity-luminosityrelation of the following form: 12 + log(O/H) = 4.059 - 0.240 M_B, with an RMSscatter of 0.252. This result implies that the slope of the metallicity-luminosity relation is steeper than when dwarf galaxies are considered alone,and may be evidence that the relationship is not linear over the fullluminosity range of the sample.Comment: 15 pages, including 7 figures and 4 tables. To appear in May, 2002 A