Direct determination of oxygen abundances in line emitting star-forming galaxies at intermediate redshift

TL;DR

This study measures oxygen abundances in 22 intermediate-redshift, metal-poor star-forming galaxies using direct spectral line diagnostics, revealing their metallicities are lower than local counterparts of similar luminosity.

Contribution

First direct oxygen abundance measurements in intermediate-redshift galaxies using auroral lines, expanding understanding of galaxy chemical evolution at these epochs.

Findings

Galaxies have metallicities between 1/10 and 1/3 solar.

They are more metal-poor than local galaxies with similar luminosity.

Properties are similar to green pea galaxies at lower redshift.

Abstract

We present a sample of 22 blue ($(B-V)_{AB}<0.45$), luminous ($M_{B,AB}<-18.9$), metal-poor galaxies in the $0.69<z<0.88$ redshift range, selected from the DEEP2 galaxy redshift survey. Their spectra contain the $[OIII]\lambda4363$ auroral line, the $[OII]\lambda \lambda3726,3729$ doublet and the strong nebular $[OIII]\lambda \lambda 4959,5007$ emission lines. The ionised gas-phase oxygen abundances of these galaxies lie between $7.62<12+\log O/H < 8.19$, i.e. between $1/10 Z_{\odot}$ and $1/3 Z_{\odot}$. We find that galaxies in our sample have comparable metallicities to other intermediate-redshift samples, but are more metal poor than local systems of similar B-band luminosities and star formation activity. The galaxies here show similar properties to the "green peas" discovered at $z\simeq 0.2 - 0.3$ though our galaxies tend to be slightly less luminous.