Properties of the Lowest Metallicity Galaxies Over the Redshift Range z = 0.2 to z = 1

TL;DR

This study identifies and characterizes extremely metal-poor galaxies at redshifts 0.2 to 1 using spectral data, revealing the lowest metallicity galaxy known at these distances and exploring their star formation properties.

Contribution

The paper reports the discovery of eight new extremely metal-poor galaxies at intermediate redshifts and refines metallicity measurements for previously known XMPGs, advancing understanding of galaxy evolution.

Findings

Discovery of the lowest metallicity galaxy at z ~ 1.

Identification of 8 new XMPGs with 12 + log O/H < 7.65.

XMPGs are best modeled by continuous starburst scenarios.

Abstract

Low-metallicity galaxies may provide key insights into the evolutionary history of galaxies. Galaxies with strong emission lines and high equivalent widths (rest-frame EW(H-beta) > 30 A) are ideal candidates for the lowest metallicity galaxies to z ~ 1. Using a Keck/DEIMOS spectral database of about 18,000 galaxies between z = 0.2 and z = 1, we search for such extreme emission-line galaxies with the goal of determining their metallicities. Using the robust direct Te method, we identify 8 new extremely metal-poor galaxies (XMPGs) with 12 + log O/H < 7.65, including one at 6.949 +/- 0.091, making it the lowest metallicity galaxy reported to date at these redshifts. We also improve upon the metallicities for two other XMPGs from previous work. We investigate the evolution of H-beta using both instantaneous and continuous starburst models, finding that XMPGs are best characterized by continuous starburst models. Finally, we study the dependence on age of the build-up of metals and the emission-line strength.