Metal Abundances of KISS Galaxies. V. Nebular Abundances of Fifteen Intermediate Luminosity Star-Forming Galaxies

TL;DR

This study provides high-quality spectroscopic data for 15 star-forming galaxies, deriving direct-method nebular abundances, comparing different temperature diagnostics, and analyzing spectral activity types to improve understanding of galaxy metallicities.

Contribution

It offers new high S/N spectra for 15 galaxies, evaluates discrepancies between abundance determination methods, and investigates the impact of different temperature diagnostics on metallicity estimates.

Findings

Oxygen abundances mostly between 8.0 and 8.3 in 12+log(O/H)

Small systematic shift in electron temperature when using sulfur lines

Discrepancies observed between direct-method and empirical abundance techniques

Abstract

We present high S/N spectroscopy of 15 emission-line galaxies (ELGs) cataloged in the KPNO International Spectroscopic Survey (KISS), selected for their possession of high equivalent width [O III] lines. The primary goal of this study was to attempt to derive direct-method ($T_e$) abundances for use in constraining the upper-metallicity branch of the $R_{23}$ relation. The spectra cover the full optical region from [O II]{\lambda}{\lambda}3726,3729 to [S III]{\lambda}{\lambda}9069,9531 and include the measurement of [O III]{\lambda}4363 in 13 objects. From these spectra, we determine abundance ratios of helium, nitrogen, oxygen, neon, sulfur, and argon. We find these galaxies to predominantly possess oxygen abundances in the range of 8.0 $\lesssim$ 12+log(O/H) $\lesssim$ 8.3. We present a comparison of direct-method abundances with empirical SEL techniques, revealing several discrepancies. We also present a comparison of direct-method oxygen abundance calculations using electron temperatures determined from emission lines of O$^{++}$ and S$^{++}$, finding a small systematic shift to lower $T_e$ (~1184 K) and higher metallicity (~0.14 dex) for sulfur-derived $T_e$ compared to oxygen-derived $T_e$. Finally, we explore in some detail the different spectral activity types of targets in our sample, including regular star-forming galaxies, those with suspected AGN contamination, and a local pair of low-metallicity, high-luminosity compact objects.