Metal Abundances of KISS Galaxies III. Nebular Abundances for Fourteen Galaxies and the Luminosity-Metallicity Relationship for HII Galaxies

Abstract

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 [OII]3727,3729 to beyond [SII]6717,6731, are presented, and abundance ratios of N, O, Ne, S, and Ar are computed. The auroral [OIII]4363 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 <= 12 + log(O/H) <= 8.32. By using these abundances in conjunction with other T_e-based measurements from the literature, we demonstrate that HII 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 HII 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 HII galaxies typically undergo factor of two luminosity enhancements, and starbursts that elevate the luminosities of their host galaxies by 2 to 3 magnitudes 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 towards 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.