Metal abundances of KISS galaxies. III. nebular abundances for fourteen galaxies and the luminosity-metallicity relationship for HII galaxies

We report results from the third in a series of nebular abundance studies of emission-line galaxies from the KPNO International Spectroscopic Survey (KISS). Galaxies with coarse metallicity estimates of 12 + log (O/H) less than 8.2 dex were selected for observation. Spectra of 14 galaxies, which cover the full optical region from[O II] lambdalambda3727, 3729 to beyond [S II] lambdalambda6717, 6731, are presented, and abundance ratios of N, O, Ne, S, and Ar are computed. The auroral [O III] lambda4363 line is detected in all 14 galaxies. Oxygen abundances determined through the direct electron temperature (T-e) method confirm that the sample is metal-poor with 7.61 less than or equal to 12 + log (O/H) less than or equal to 8.32. By using these abundances in conjunction with other T-e-based measurements from the literature, we demonstrate that H II galaxies and more quiescent dwarf irregular galaxies follow similar metallicity-luminosity (L-Z) relationships. The primary difference is a zero-point shift between the correlations such that H II galaxies are brighter by an average of 0.8 B magnitudes at a given metallicity. This offset can be used as evidence to argue that low-luminosity H II galaxies typically undergo factor of 2 luminosity enhancements, and starbursts that elevate the luminosities of their host galaxies by 2-3 mag are not as common. We also demonstrate that the inclusion of interacting galaxies can increase the scatter in the L-Z relation and may force the observed correlation toward lower metallicities and/or larger luminosities. This must be taken into account when attempting to infer metal abundance evolution by comparing local L-Z relations with ones based on higher redshift samples, since the fraction of interacting galaxies should increase with look-back time.