The Grism Lens-Amplified Survey from Space (GLASS). II. Gas-phase metallicity and radial gradients in an interacting system at z~2

TL;DR

This study uses gravitational lensing and HST spectroscopy to measure spatially resolved gas-phase metallicity and gradients in three interacting galaxies at z~2, revealing flattened metallicity gradients likely due to gravitational interactions.

Contribution

It provides the first precise metallicity gradient measurement in low-mass, high-redshift galaxies, demonstrating the potential of lensing and HST for studying galaxy evolution at small scales.

Findings

Shallow metallicity gradient in an interacting galaxy at z~2.

Gas-phase metallicities consistent with similar high-redshift samples.

Probing stellar masses down to 10^7.2 Msun, comparable to local dwarf galaxies.

Abstract

We present spatially resolved gas-phase metallicity for a system of three galaxies at z=1.85 detected in the Grism Lens-Amplified Survey from Space (GLASS). The combination of HST's diffraction limit and strong gravitational lensing by the cluster MACS J0717+3745 results in a spatial resolution of ~200-300 pc, enabling good spatial sampling despite the intrinsically small galaxy sizes. The galaxies in this system are separated by 50-200 kpc in projection and are likely in an early stage of interaction, evidenced by relatively high specific star formation rates. Their gas-phase metallicities are consistent with larger samples at similar redshift, star formation rate, and stellar mass. We obtain a precise measurement of the metallicity gradient for one galaxy and find a shallow slope compared to isolated galaxies at high redshift, consistent with a flattening of the gradient due to gravitational interaction. An alternative explanation for the shallow metallicity gradient and elevated star formation rate is rapid recycling of metal-enriched gas, but we find no evidence for enhanced gas-phase metallicities which should result from this effect. Notably, the measured stellar masses log(M/Msun) = 7.2-9.1 probe to an order of magnitude below previous mass-metallicity studies at this redshift. The lowest mass galaxy has properties similar to those expected for Fornax at this redshift, indicating that GLASS is able to directly study the progenitors of local group dwarf galaxies on spatially resolved scales. Larger samples from the full GLASS survey will be ideal for studying the effects of feedback, and the time evolution of metallicity gradients. These initial results demonstrate the utility of HST spectroscopy combined with gravitational lensing for characterizing resolved physical properties of galaxies at high redshift.