Testing the Universality of the Fundamental Metallicity Relation at High Redshift Using Low-Mass Gravitationally Lensed Galaxies

TL;DR

This study confirms that the fundamental metallicity relation between stellar mass, metallicity, and star formation rate holds at high redshift for low-mass galaxies, showing minimal scatter and suggesting universality.

Contribution

First direct spectroscopic confirmation that the fundamental metallicity relation applies at high redshift for low-mass galaxies using gravitational lensing.

Findings

High-redshift low-mass galaxies follow the local fundamental metallicity relation.

The scatter around the relation at high redshift is smaller than locally.

The relation's universality constrains galaxy evolution models.

Abstract

We present rest-frame optical spectra for a sample of 9 low-mass star-forming galaxies in the redshift range 1.5 < z < 3 which are gravitationally lensed by foreground clusters. We used Triplespec, an echelle spectrograph at the Palomar 200-inch telescope that is very effective for this purpose as it samples the entire near-infrared spectrum simultaneously. By measuring the flux of nebular emission lines we derive gas phase metallicities and star formation rates, and by fitting the optical to infrared spectral energy distributions we obtain stellar masses. Taking advantage of the high magnification due to strong lensing we are able to probe the physical properties of galaxies with stellar masses in the range 7.8 < log M/Msun < 9.4 whose star formation rates are similar to those of typical star-forming galaxies in the local universe. We compare our results with the locally determined relation between stellar mass, gas metallicity and star formation rate. Our data are in excellent agreement with this relation, with an average offset <Delta log O/H> = 0.01 +/- 0.08, suggesting a universal relationship. Remarkably, the scatter around the fundamental metallicity relation is only 0.24 dex, smaller than that observed locally at the same stellar masses, which may provide an important additional constraint for galaxy evolution models.