First direct metallicity measurement of a lensed star-forming galaxy at z=1.7

TL;DR

This study reports the first direct metallicity measurement of a lensed star-forming galaxy at z=1.7 using the auroral line [O III] 4363, revealing an extremely low metallicity and extending the luminosity-metallicity relation.

Contribution

It provides the first direct metallicity measurement for a galaxy at z>1, using the auroral line, and characterizes its properties and potential merger status.

Findings

Galaxy has extremely low metallicity.

Extends luminosity-metallicity relation to higher redshifts.

Possible merger or proto-rotating disk morphology.

Abstract

We present the rest-frame optical spectrum of a strongly lensed galaxy at redshift z =1.7 behind the cluster Abell 1689. We detect the temperature sensitive auroral line [O III] 4363, which allows the first direct metallicity measurement for galaxies at z > 1. Our high signal-to-noise spectrum indicates that the target is an extremely low metallicity star-forming galaxy.We estimate an intrinsic absolute B band magnitude of M_{B}=-18.3 \pm 0.1$, with a stellar mass of 4.4$\pm1.2\times10^{8}$ M$_{\odot}$. This galaxy extends the luminosity-metallicity relation of star-forming galaxies at z > 2 by more than an order of magnitude. Given the double-nuclei like morphology and velocity profile of \ha, we tentatively suggest that it could be a merger or a proto-rotating disk galaxy.